AC_PROG_LIBTOOL changing ./configure compiler selection

[Guillaume Rousse]

I'm trying to convert a program creating static libraries only to
libtool use. In configure.ac, I just changed AC_PROG_RANLIB to
AC_PROG_LIBTOOL. However, as a side-effect, configure script tries to
use gcc instead of g++, and fails to find correct headers.

The initial configure.ac looks like:
AC_PROG_CC(cc gcc)
AC_PROG_CXX(CC g++ gcc c++ cxx)
AC_PROG_F77(f77 g77 f90 xlf90)
AC_PROG_RANLIB
...
AC_CHECK_HEADERS([cstdlib stdlib.h], [break],)

In the normal case, all headers are checked through g++:
configure:4874: checking for stdlib.h
configure:4890: i586-mandriva-linux-gnu-g++ -c -O2 -g -pipe
-Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fomit-frame-pointer -march=i586
-mtune=pentiumpro -fasynchronous-unwind-tables  conftest.cc >&5
configure:4896: $? = 0

In the modified case, all headers are checked throug gcc:
configure:20426: checking cstdlib usability
configure:20438: i586-mandriva-linux-gnu-gcc -c -O2 -g -pipe
-Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fomit-frame-pointer -march=i586
-mtune=pentiumpro -fasynchronous-unwind-tables  conftest.c >&5
conftest.c:59:19: error: cstdlib: No such file or directory
configure:20444: $? = 1

Comparative examination of both config  log is OK until AC_PROG_F77()
result, then AC_PROG_LIBTOOL seems to have a bunch of specific checks,
using gcc, such as:
configure:4336: checking for ld used by i586-mandriva-linux-gnu-gcc

I'm using libtool 1.5.20, automake 1.9.6 and autoconf 2.59 on mandriva
linux. Both config.log files are available as:
http://www.zarb.org/~guillomovitch/config.log.ok
http://www.zarb.org/~guillomovitch/config.log.nok