configure: move to AC_COMPILE_IFELSE

from AC_PREPROC_IFELSE which is strongly discouraged.

Our detection system was very weak and recent versions of clang did
show that PREPROC_IFELFE (cpp) would enable warning options that
the compiler does not support (clang).

Use a full compilation test to detect what works and what doesn't.

Based on knet patch 88491f27375a9e8aceb946853a1abf4d23ebb8f3.

Signed-off-by: Jan Friesse <jfriesse@redhat.com>
Reviewed-by: Fabio M. Di Nitto <fdinitto@redhat.com>

diff --git a/configure.ac b/configure.ac
index e6954df45d42fc2a1d73337d7697bfdf2e57ca39..cd3a58d36cf76ec7e61a7ec03f39e1af801970c4 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -112,7 +112,7 @@ cc_supports_flag() {
        BACKUP="$CPPFLAGS"
        CPPFLAGS="$CPPFLAGS $@ $unknown_warnings_as_errors"
        AC_MSG_CHECKING([whether $CC supports "$@"])
-       AC_PREPROC_IFELSE([AC_LANG_PROGRAM([])],
+       AC_COMPILE_IFELSE([AC_LANG_PROGRAM([])],
                          [RC=0; AC_MSG_RESULT([yes])],
                          [RC=1; AC_MSG_RESULT([no])])
        CPPFLAGS="$BACKUP"