Perl compilation/link flags for building XSParagraph

[Eli Zaretskii]

The configure script's help says near its end:

  PERL_EXT_CFLAGS
              Compiler flags for a Perl extension
  PERL_EXT_CPPFLAGS
              C preprocessor flags for a Perl extension
  PERL_EXT_LDFLAGS
              Linker flags for a Perl extension

The Makefile created in tp/Texinfo/Convert/XSParagraph leaves these
variables undefined, so that they could be set by the user:

  # PERL_EXT_var are user variables, allowing configuring at the top-level 
  # with e.g. "./configure CFLAGS='-g -O0' PERL_EXT_CFLAGS='-g'".

The Makefile then inserts the values of these variables into the
corresponding libtool commands, e.g.:

  LDFLAGS = $(PERL_EXT_LDFLAGS)

I needed to use PERL_EXT_LDFLAGS today, in order to pass
"-static-libgcc" to GCC (thus avoiding run-time dependency on the
libgcc shared library, which gets in the way when building Texinfo on
onesystem, then installing the binaries on another).  I found that the
switch is being ignored in the link command to build the XSParagraph
shared library.

After some digging, it turns out that libtool ignores any switches it
doesn't understand when issuing the link command.  The usual trick for
this is to configure with CC='gcc -static-libgcc' (because the value
of $CC does get used verbatim by libtool).  However, in this
particular case, this trick doesn't work, because the configure script
in tp/Texinfo/Convert/XSParagraph forcefully ignores the top-level
value of CC, since it needs to use the compiler requested by Perl.

I found no way out of this conundrum, and ended up editing the libtool
script by hand to inject -static-libgcc into the value of CC it
records.

Bottom line, I think that the XSParagraph configure script should
append the value of PERL_EXT_LDFLAGS to the value of CC it uses when
it builds the libtool script, because otherwise most values of that
variable will have no effect.  Not sure if the same problem exists
with PERL_EXT_CFLAGS and PERL_EXT_CPPFLAGS.

Thanks.