Suppress some unhelpful warnings when using clang.

* configure.ac: With clang, check for and use -Wno-switch,
-Wno-tautological-constant-out-of-range-compare and -Wno-pointer-sign.

* conf_post.h(assume): Use __builtin_unreachable for clang.

* src/filelock.c (lock_file_1): Rearrange to remove compiler warning
about excess arguments to snprintf.

1 files changed, 18 insertions, 10 deletions

diff --git a/configure.ac b/configure.ac
index c63627d18d4..16259f01ed2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -787,10 +787,28 @@ AC_DEFUN([gl_GCC_VERSION_IFELSE],
   ]
 )
 
+# clang is unduly picky about some things.
+AC_CACHE_CHECK([whether the compiler is clang], [emacs_cv_clang],
+  [AC_COMPILE_IFELSE(
+     [AC_LANG_PROGRAM([[
+	  #ifndef __clang__
+	    #error "not clang"
+	  #endif
+        ]])],
+     [emacs_cv_clang=yes],
+     [emacs_cv_clang=no])])
+
 # When compiling with GCC, prefer -isystem to -I when including system
 # include files, to avoid generating useless diagnostics for the files.
 if test "$gl_gcc_warnings" != yes; then
   isystem='-I'
+  if test "$emacs_cv_clang" = yes
+  then
+     # Turn off some warnings if supported.
+     gl_WARN_ADD([-Wno-switch])
+     gl_WARN_ADD([-Wno-tautological-constant-out-of-range-compare])
+     gl_WARN_ADD([-Wno-pointer-sign])
+  fi
 else
   isystem='-isystem '
 
@@ -840,16 +858,6 @@ else
   nw="$nw -Wtype-limits"
   nw="$nw -Wunused-parameter"
 
-  # clang is unduly picky about some things.
-  AC_CACHE_CHECK([whether the compiler is clang], [emacs_cv_clang],
-    [AC_COMPILE_IFELSE(
-       [AC_LANG_PROGRAM([[
-	    #ifndef __clang__
-	      #error "not clang"
-	    #endif
-          ]])],
-       [emacs_cv_clang=yes],
-       [emacs_cv_clang=no])])
   if test $emacs_cv_clang = yes; then
     nw="$nw -Wcast-align"
   fi