Drop unsupported -Wno-stringop-truncation when building with clang.

(cherry picked from commit 2ac77e1)

Author: petterreinholdtsen

src/Makefile

@@ -252,7 +252,7 @@ INCLUDE += $(LIBTIRPC_CFLAGS)
 # Compilation options.	Perhaps some of these should come from Makefile.inc? (CXXFLAGS now does)
 INTEGER_OVERFLOW_FLAGS := -fwrapv
 OPT := -Os $(INTEGER_OVERFLOW_FLAGS)
-DEBUG := $(DEBUG) -g -Wall -Wno-stringop-truncation -D_FORTIFY_SOURCE=2
+DEBUG := $(DEBUG) -g -Wall -D_FORTIFY_SOURCE=2
 CFLAGS := $(INCLUDE) $(OPT) $(DEBUG) $(EXTRA_DEBUG) -DULAPI -std=gnu11 -Werror=implicit-function-declaration $(CFLAGS) $(CPPFLAGS)
 CXXFLAGS := $(INCLUDE) $(EXTRA_DEBUG) -DULAPI $(DEBUG) $(OPT) -Werror=overloaded-virtual $(CXXFLAGS) $(CPPFLAGS)
 CXXFLAGS += -std=gnu++17

src/configure.ac

@@ -408,6 +408,14 @@ elif ! test `$CC -dumpversion | cut -d '.' -f 1` -gt 2 ; then
   AC_MSG_ERROR([Compilers older than gcc 3.x are no longer supported])
 fi
 
+# Set flags for C and C++ if supported
+for commonflag in -Wno-stringop-truncation ; do
+  if echo "int main() { return 0;}" | $CC -Werror $commonflag -E - > /dev/null; then
+    CFLAGS="$CFLAGS $flag"
+    CXXFLAGS="$CXXFLAGS $flag"
+  fi
+done
+
 AC_MSG_CHECKING([for usability of linux/hidraw.h])
 AC_LINK_IFELSE([AC_LANG_PROGRAM([[
 #include <sys/ioctl.h>