meson: also reject shifts that change the sign bit

../src/test/test-sizeof.c: In function ‘main’:
../src/test/test-sizeof.c:70:24: error: result of ‘1 << 31’ requires 33 bits to represent, but ‘int’ only has 32 bits [-Werror=shift-overflow=]
                 X = (1 << 31),
                        ^~
cc1: some warnings being treated as errors

Follow-up for b05ecb8cadd8c32d31b1aabcff4e507bd89b5465.

meson.build

@@ -320,6 +320,7 @@ possible_cc_flags = [
         '-Wwrite-strings',
         '-Werror=overflow',
         '-Werror=shift-count-overflow',
+        '-Werror=shift-overflow=2',
         '-Wdate-time',
         '-Wnested-externs',
         '-ffast-math',