ac_check_cc_opt

AC_CHECK_CC_OPT(-fvomit-frame,vomitframe) would show a message as like "checking wether gcc accepts -fvomit-frame ... no" and sets the shell-variable $vomitframe to either "-fvomit-frame" or (in this case) just a simple "". In many cases you would then call AC_SUBST(_fvomit_frame_,$vomitframe) to create a substitution that could be fed as "CFLAGS = @_funsigned_char_@ @_fvomit_frame_@

in consequence this function is much more general than their specific counterparts like ac_cxx_rtti.m4 that will test for -fno-rtti -fno-exceptions

this macro will be obsolete in the very near future - there should be two macros AX_CFLAGS_OPTION and AX_CXXFLAGS_OPTION that will add directly to the CFLAGS/CXXFLAGS unless a ac_subst-variable was given. Remind me of doing so if I forget about writing it all up - to use $CC-cc directly in here instead of ac_compile macro is bad anyway.

AC_DEFUN([AC_CHECK_CC_OPT],
[AC_CACHE_CHECK(whether ${CC-cc} accepts [$1], [$2],
[AC_SUBST($2)
echo 'void f(){}' > conftest.c
if test -z "`${CC-cc} -c $1 conftest.c 2>&1`"; then
  $2="$1"
else
  $2=""
fi
rm -f conftest*
])])