Bug 1323923 - Part 2: Suppress more clang warnings and unify CLANG_CXX/CLANG_CL warning flags in gfx/cairo. r=lsalzman

gfx/cairo/cairo/src/cairo-image-surface.c:1225:35 [-Wabsolute-value] using floating point absolute value function 'fabs' when argument is of integer type
gfx/cairo/cairo/src/cairo-image-surface.c:1227:35 [-Wabsolute-value] using floating point absolute value function 'fabs' when argument is of integer type
gfx/cairo/cairo/src/cairo-quartz-surface.c:1919:12 [-Wunreachable-code] code will never be executed
gfx/cairo/cairo/src/cairo-quartz-surface.c:1920:6 [-Wunreachable-code] code will never be executed
gfx/cairo/cairo/src/cairo-quartz-surface.c:3530:18 [-Wunused-variable] unused variable 'i'
gfx/cairo/cairo/src/cairo-version.c:39:9 [-Wmacro-redefined] 'CAIRO_VERSION_H' macro redefined

gfx/cairo/cairo/src/moz.build

@@ -224,18 +224,17 @@ if CONFIG['GNU_CC'] or CONFIG['CLANG_CL']:
         '-Wno-conversion',
         '-Wno-unused',
     ]
+
 if CONFIG['CLANG_CXX'] or CONFIG['CLANG_CL']:
     CFLAGS += [
+        '-Wno-absolute-value',
+        '-Wno-deprecated-register',
         '-Wno-incompatible-pointer-types',
+        '-Wno-macro-redefined',
         '-Wno-tautological-compare',
         '-Wno-tautological-constant-out-of-range-compare',
         '-Wno-error=uninitialized',
     ]
-if CONFIG['CLANG_CL']:
-    CFLAGS += [
-        '-Wno-deprecated-register',
-        '-Wno-macro-redefined',
-    ]
 
 # See bug 386897.
 if CONFIG['GNU_CC'] and CONFIG['OS_TARGET'] == 'Android' and CONFIG['MOZ_OPTIMIZE']: