Port --enable-gcc-warnings to clang 3.9.1

* configure.ac (WERROR_CFLAGS): Omit -Wdouble-promotion if clang.
Problem reported by Philipp Stephani in:
http://lists.gnu.org/archive/html/emacs-devel/2017-05/msg00495.html

diff --git a/configure.ac b/configure.ac
index 34b75a768bf84c28925f7589630664e9c18b9538..03542a6b1c30951c5f38fc0cd5a1ac7d7200713d 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -963,6 +963,7 @@ AS_IF([test $gl_gcc_warnings = no],
 
   if test $emacs_cv_clang = yes; then
     nw="$nw -Wcast-align"
+    nw="$nw -Wdouble-promotion"
   fi
 
   # This causes too much noise in the MinGW build