doc: mention some declaration fixes

[Bruno Haible]

Strangely enough, the modules 'chdir' and 'read' were not mentioned in the
function substitutes documentation. This patch fixes it.


2020-06-26  Bruno Haible  <bruno@clisp.org>

        doc: Mention declaration fixes implemented by some modules.
        * doc/posix-functions/chdir.texi: Mention the module 'chdir'.
        * doc/posix-functions/close.texi: Mention that Gnulib makes the function
        declaration appear in <unistd.h>.
        * doc/posix-functions/dup.texi: Likewise.
        * doc/posix-functions/dup2.texi: Likewise.
        * doc/posix-functions/gethostname.texi: Likewise.
        * doc/posix-functions/isatty.texi: Likewise.
        * doc/posix-functions/lseek.texi: Likewise.
        * doc/posix-functions/unlink.texi: Likewise.
        * doc/posix-functions/read.texi: Mention the module 'read'.
        * doc/posix-functions/write.texi: Mention the effects of the module
        'write'.

diff --git a/doc/posix-functions/chdir.texi b/doc/posix-functions/chdir.texi
index 9a65578..3963271 100644
--- a/doc/posix-functions/chdir.texi
+++ b/doc/posix-functions/chdir.texi
@@ -4,7 +4,7 @@
 
 POSIX specification:@* 
@url{https://pubs.opengroup.org/onlinepubs/9699919799/functions/chdir.html}
 
-Gnulib module: ---
+Gnulib module: chdir
 
 Portability problems fixed by Gnulib:
 @itemize
diff --git a/doc/posix-functions/close.texi b/doc/posix-functions/close.texi
index 9f9f66c..58f8e9a 100644
--- a/doc/posix-functions/close.texi
+++ b/doc/posix-functions/close.texi
@@ -9,6 +9,10 @@ Gnulib module: close
 Portability problems fixed by Gnulib:
 @itemize
 @item
+This function is declared in a different header file (namely, @code{<io.h>})
+on some platforms:
+MSVC 14.
+@item
 This function crashes when invoked with invalid arguments on some platforms:
 MSVC 14.
 @item
diff --git a/doc/posix-functions/dup.texi b/doc/posix-functions/dup.texi
index e57a8d5..c43ba8c 100644
--- a/doc/posix-functions/dup.texi
+++ b/doc/posix-functions/dup.texi
@@ -9,6 +9,10 @@ Gnulib module: dup
 Portability problems fixed by Gnulib:
 @itemize
 @item
+This function is declared in a different header file (namely, @code{<io.h>})
+on some platforms:
+MSVC 14.
+@item
 This function crashes when invoked with invalid arguments on some platforms:
 MSVC 14.
 @end itemize
diff --git a/doc/posix-functions/dup2.texi b/doc/posix-functions/dup2.texi
index c7bc212..8635e6c 100644
--- a/doc/posix-functions/dup2.texi
+++ b/doc/posix-functions/dup2.texi
@@ -9,6 +9,11 @@ Gnulib module: dup2 or dup2-obsolete
 Portability problems fixed by either Gnulib module @code{dup2} or 
@code{dup2-obsolete}:
 @itemize
 @item
+This function is declared in a different header file (namely, @code{<io.h>})
+on some platforms:
+MSVC 14.
+
+@item
 This function always returns 0 for success on some platforms:
 mingw, MSVC 14.
 
diff --git a/doc/posix-functions/gethostname.texi 
b/doc/posix-functions/gethostname.texi
index a7ff3f6..d162cea 100644
--- a/doc/posix-functions/gethostname.texi
+++ b/doc/posix-functions/gethostname.texi
@@ -9,6 +9,10 @@ Gnulib module: gethostname
 Portability problems fixed by Gnulib:
 @itemize
 @item
+This function is declared in a different header file (namely,
+@code{<winsock2.h>}) on some platforms:
+MSVC 14.
+@item
 On mingw and MSVC 14, this function has a prototype that differs from that
 specified by POSIX, and it is defined only in the ws2_32 library.
 @end itemize
diff --git a/doc/posix-functions/isatty.texi b/doc/posix-functions/isatty.texi
index 29eee74..d01f8e3 100644
--- a/doc/posix-functions/isatty.texi
+++ b/doc/posix-functions/isatty.texi
@@ -9,6 +9,10 @@ Gnulib module: isatty
 Portability problems fixed by Gnulib:
 @itemize
 @item
+This function is declared in a different header file (namely, @code{<io.h>})
+on some platforms:
+MSVC 14.
+@item
 On native Windows, this function also returns true for character devices such
 as @file{NUL}.
 @item
diff --git a/doc/posix-functions/lseek.texi b/doc/posix-functions/lseek.texi
index f5f06ce..4a9d55d 100644
--- a/doc/posix-functions/lseek.texi
+++ b/doc/posix-functions/lseek.texi
@@ -9,6 +9,10 @@ Gnulib module: lseek
 Portability problems fixed by Gnulib:
 @itemize
 @item
+This function is declared in a different header file (namely, @code{<io.h>})
+on some platforms:
+MSVC 14.
+@item
 On platforms where @code{off_t} is a 32-bit type, @code{lseek} does not work
 correctly with files larger than 2 GB@.  (Cf. @code{AC_SYS_LARGEFILE}.)
 @item
diff --git a/doc/posix-functions/read.texi b/doc/posix-functions/read.texi
index 901470f..a48e5ea 100644
--- a/doc/posix-functions/read.texi
+++ b/doc/posix-functions/read.texi
@@ -4,13 +4,21 @@
 
 POSIX specification:@* 
@url{https://pubs.opengroup.org/onlinepubs/9699919799/functions/read.html}
 
-Gnulib module: stdio, nonblocking
+Gnulib module: read, stdio, nonblocking
 
-Portability problems fixed by Gnulib module @code{stdio}, together with module 
@code{nonblocking}:
+Portability problems fixed by Gnulib module @code{read}:
 @itemize
 @item
+This function is declared in a different header file (namely, @code{<io.h>})
+on some platforms:
+mingw, MSVC 14.
+@item
 This function crashes when invoked with invalid arguments on some platforms:
 MSVC 14.
+@end itemize
+
+Portability problems fixed by Gnulib module @code{stdio}, together with module 
@code{nonblocking}:
+@itemize
 @item
 When reading from a non-blocking pipe whose buffer is empty, this function
 fails with @code{errno} being set to @code{EINVAL} instead of @code{EAGAIN} on
diff --git a/doc/posix-functions/unlink.texi b/doc/posix-functions/unlink.texi
index 4ee0003..15cfd84 100644
--- a/doc/posix-functions/unlink.texi
+++ b/doc/posix-functions/unlink.texi
@@ -9,6 +9,10 @@ Gnulib module: unlink
 Portability problems fixed by Gnulib:
 @itemize
 @item
+This function is declared in a different header file (namely, @code{<stdio.h>})
+on some platforms:
+MSVC 14.
+@item
 Some systems mistakenly succeed on @code{unlink("link-to-file/")}:
 GNU/Hurd, FreeBSD 7.2, AIX 7.1, Solaris 9.
 @item
diff --git a/doc/posix-functions/write.texi b/doc/posix-functions/write.texi
index 1ff9021..e3042a5 100644
--- a/doc/posix-functions/write.texi
+++ b/doc/posix-functions/write.texi
@@ -6,11 +6,19 @@ POSIX specification:@* 
@url{https://pubs.opengroup.org/onlinepubs/9699919799/fun
 
 Gnulib module: write, nonblocking, sigpipe
 
-Portability problems fixed by Gnulib module @code{stdio}, together with module 
@code{nonblocking}:
+Portability problems fixed by Gnulib module @code{write}:
 @itemize
 @item
+This function is declared in a different header file (namely, @code{<io.h>})
+on some platforms:
+mingw, MSVC 14.
+@item
 This function crashes when invoked with invalid arguments on some platforms:
 MSVC 14.
+@end itemize
+
+Portability problems fixed by Gnulib module @code{stdio}, together with module 
@code{nonblocking}:
+@itemize
 @item
 When writing to a non-blocking pipe whose buffer is full, this function fails
 with @code{errno} being set to @code{ENOSPC} instead of @code{EAGAIN} on some