get-rusage-data: Fix link error on FreeBSD 12.2/arm64

[Bruno Haible]

On FreeBSD 12.2/arm64, the brk() and sbrk() functions no longer exist [1].
This causes a link error in module get-rusage-data.

This patch fixes it.

[1] https://www.freebsd.org/cgi/man.cgi?query=sbrk&sektion=2


2020-12-07  Bruno Haible  <bruno@clisp.org>

        get-rusage-data: Fix link error on FreeBSD 12.2/arm64.
        * modules/get-rusage-data (configure.ac): Test whether sbrk exists.
        * lib/get-rusage-data.c (get_rusage_data_via_setrlimit): Define
        trivially of sbrk is not available.
        * doc/glibc-functions/sbrk.texi: Mention that the function does not
        exist in FreeBSD 12.2/arm64.
        * doc/glibc-functions/brk.texi: Likewise.

diff --git a/doc/glibc-functions/brk.texi b/doc/glibc-functions/brk.texi
index bc046ca..2ca966d 100644
--- a/doc/glibc-functions/brk.texi
+++ b/doc/glibc-functions/brk.texi
@@ -25,5 +25,5 @@ Portability problems not fixed by Gnulib:
 @itemize
 @item
 This function is missing on some platforms:
-AIX 5.1, Cygwin 2.9, mingw, MSVC 14.
+FreeBSD 12.2/arm64, AIX 5.1, Cygwin 2.9, mingw, MSVC 14.
 @end itemize
diff --git a/doc/glibc-functions/sbrk.texi b/doc/glibc-functions/sbrk.texi
index 8a3d5ab..c09459f 100644
--- a/doc/glibc-functions/sbrk.texi
+++ b/doc/glibc-functions/sbrk.texi
@@ -14,5 +14,5 @@ Portability problems not fixed by Gnulib:
 @itemize
 @item
 This function is missing on some platforms:
-AIX 5.1, mingw, MSVC 14.
+FreeBSD 12.2/arm64, AIX 5.1, mingw, MSVC 14.
 @end itemize
diff --git a/lib/get-rusage-data.c b/lib/get-rusage-data.c
index 411be94..234442c 100644
--- a/lib/get-rusage-data.c
+++ b/lib/get-rusage-data.c
@@ -150,7 +150,7 @@
 #if !(defined __APPLE__ && defined __MACH__) || defined TEST
 /* Implement get_rusage_data_via_setrlimit().  */
 
-# if HAVE_SETRLIMIT && defined RLIMIT_DATA && !defined __HAIKU__
+# if HAVE_SETRLIMIT && defined RLIMIT_DATA && HAVE_SBRK && !defined __HAIKU__
 
 #  ifdef _AIX
 #   define errno_expected() (errno == EINVAL || errno == EFAULT)
@@ -166,9 +166,9 @@ get_rusage_data_via_setrlimit (void)
   struct rlimit orig_limit;
 
 #  ifdef __hpux
-  /* On HP-UX 11.00, setrlimit() RLIMIT_DATA of does not work: It cannot
+  /* On HP-UX 11.00, setrlimit() of RLIMIT_DATA does not work: It cannot
      restore the previous limits.
-     On HP-UX 11.11, setrlimit() RLIMIT_DATA of does not work: It sometimes
+     On HP-UX 11.11, setrlimit() of RLIMIT_DATA does not work: It sometimes
      has no effect on the next sbrk() call.  */
   {
     struct utsname buf;
diff --git a/modules/get-rusage-data b/modules/get-rusage-data
index 6840116..4206ec9 100644
--- a/modules/get-rusage-data
+++ b/modules/get-rusage-data
@@ -14,7 +14,7 @@ getpagesize
 vma-iter
 
 configure.ac:
-AC_CHECK_FUNCS_ONCE([setrlimit])
+AC_CHECK_FUNCS_ONCE([sbrk setrlimit])
 gl_FUNC_MMAP_ANON
 
 Makefile.am: