Add some news CFLAGS:

* -Wpragmas
* -Wunreachable-code
* -Wpedantic
* -Waddress
* -Wattributes
* -Wdiv-by-zero
* -Wheader-guard

configure.ac

@@ -448,6 +448,14 @@ if test "x$werror" != "xno"; then
     AX_CHECK_COMPILE_FLAG([-Wclobbered], [CFLAGS="$CFLAGS -Wclobbered"])
     AX_CHECK_COMPILE_FLAG([-Wvla], [CFLAGS="$CFLAGS -Wvla"])
     AX_CHECK_COMPILE_FLAG([-Wno-unused-parameter], [CFLAGS="$CFLAGS -Wno-unused-parameter"])
+    AX_CHECK_COMPILE_FLAG([-Wpragmas], [CFLAGS="$CFLAGS -Wpragmas"])
+    AX_CHECK_COMPILE_FLAG([-Wunreachable-code], [CFLAGS="$CFLAGS -Wunreachable-code"])
+    AX_CHECK_COMPILE_FLAG([-Waddress], [CFLAGS="$CFLAGS -Waddress"])
+    AX_CHECK_COMPILE_FLAG([-Wattributes], [CFLAGS="$CFLAGS -Wattributes"])
+    AX_CHECK_COMPILE_FLAG([-Wdiv-by-zero], [CFLAGS="$CFLAGS -Wdiv-by-zero"])
+
+    # Only work with Clang for the moment
+    AX_CHECK_COMPILE_FLAG([-Wheader-guard], [CFLAGS="$CFLAGS -Wheader-guard"])
 fi
 
 if test "x$debug" != "xno"; then