[gnome-builder] build: improve clang/llvm check

[Christian Hergert <chergert src gnome org>]

commit efb13f0acf26ae5af148e6b520012503233c60b9
Author: Christian Hergert <christian hergert me>
Date:   Wed Feb 11 23:34:31 2015 -0800

    build: improve clang/llvm check

 build/autotools/autoconf.d/50_dependencies.post-am |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)
---
diff --git a/build/autotools/autoconf.d/50_dependencies.post-am 
b/build/autotools/autoconf.d/50_dependencies.post-am
index 129b8d1..4d3b815 100644
--- a/build/autotools/autoconf.d/50_dependencies.post-am
+++ b/build/autotools/autoconf.d/50_dependencies.post-am
@@ -16,7 +16,11 @@ PKG_CHECK_MODULES(LIBIDE, [gio-2.0 >= glib_required_version
 
 AC_PATH_PROG([LLVM_CONFIG], [llvm-config])
 AS_IF([test "x$LLVM_CONFIG" = "x"],[
-    AC_MSG_ERROR([Failed to locate the llvm-config program.])
+    AC_MSG_ERROR([Failed to locate the llvm-config program. Please install llvm-devel.])
 ])
 CLANG_LDFLAGS=`$LLVM_CONFIG --ldflags`
 AC_SUBST([CLANG_LDFLAGS])
+
+AC_CHECK_HEADER([clang-c/Index.h], [], [
+    AC_MSG_ERROR([Failed to locage clang-c/Index.h. Please install clang-devel.])
+])