[PATCH 2/3] build: Check for -Wtrampolines support

[tbaeder@redhat.com]

From: Timm Bäder <tbaeder@redhat.com>

Clang does not support -Wtrampolines, so check if the compiler supports
it before using it.

Signed-off-by: Timm Bäder <tbaeder@redhat.com>
---
 config/eu.am | 10 ++++++++--
 configure.ac |  9 +++++++++
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/config/eu.am b/config/eu.am
index e109ffd3..02512570 100644
--- a/config/eu.am
+++ b/config/eu.am
@@ -73,8 +73,14 @@ else
 IMPLICIT_FALLTHROUGH_WARNING=
 endif
 
+if HAVE_TRAMPOLINES_WARNING
+TRAMPOLINES_WARNING=-Wtrampolines
+else
+TRAMPOLINES_WARNING=
+endif
+
 AM_CFLAGS = -std=gnu99 -Wall -Wshadow -Wformat=2 \
-	    -Wold-style-definition -Wstrict-prototypes -Wtrampolines \
+	    -Wold-style-definition -Wstrict-prototypes $(TRAMPOLINES_WARNING) \
 	    $(LOGICAL_OP_WARNING) $(DUPLICATED_COND_WARNING) \
 	    $(NULL_DEREFERENCE_WARNING) $(IMPLICIT_FALLTHROUGH_WARNING) \
 	    $(if $($(*F)_no_Werror),,-Werror) \
@@ -84,7 +90,7 @@ AM_CFLAGS = -std=gnu99 -Wall -Wshadow -Wformat=2 \
 	    $($(*F)_CFLAGS)
 
 AM_CXXFLAGS = -std=c++11 -Wall -Wshadow \
-	   -Wtrampolines \
+	   $(TRAMPOLINES_WARNING) \
 	   $(LOGICAL_OP_WARNING) $(DUPLICATED_COND_WARNING) \
 	   $(NULL_DEREFERENCE_WARNING) $(IMPLICIT_FALLTHROUGH_WARNING) \
 	   $(if $($(*F)_no_Werror),,-Werror) \
diff --git a/configure.ac b/configure.ac
index e56aeb6a..5f3321aa 100644
--- a/configure.ac
+++ b/configure.ac
@@ -537,6 +537,15 @@ if test "$ac_cv_implicit_fallthrough" = "yes"; then
 		  [Defined if __attribute__((fallthrough)) is supported])
 fi
 
+AC_CACHE_CHECK([whether the compiler accepts -Wtrampolines], ac_cv_trampolines, [dnl
+old_CFLAGS="$CFLAGS"
+CFLAGS="$CFLAGS -Wtrampolines -Werror"
+AC_COMPILE_IFELSE([AC_LANG_SOURCE([])],
+		  ac_cv_trampolines=yes, ac_cv_trampolines=no)
+CFLAGS="$old_CFLAGS"])
+AM_CONDITIONAL(HAVE_TRAMPOLINES_WARNING,
+	       [test "x$ac_cv_trampolines" != "xno"])
+
 saved_LIBS="$LIBS"
 AC_SEARCH_LIBS([argp_parse], [argp])
 LIBS="$saved_LIBS"
-- 
2.26.2