Re: __builtin_mul_overflow_p support with llvm 5.0

[Paul Eggert]

Paul Eggert wrote:
> Sorry, what's the context here?

Ah, I see it now, here:

https://github.com/coreutils/coreutils/issues/11

where Bernhard Rosenkränzer wrote:

"Our clang package is (intentionally) patched to return GNUC == 7 because clang 
5.0 is closer to gcc 7.x than to any other version of gcc"

That's the problem. A goodly amount of GNU code assumes that if __GNUC__ is 5 
then your compiler supports the features of GCC 5 or later, and similarly for 
other values of __GNUC__. Since your implementation of Clang does not support 
all relevant GCC 7 features, it should not define __GNUC__ to 7. So I suggest 
reverting the patch that you mentioned.

This problem is not limited to the two Gnulib modules that you mention: it's in 
several other places in GNU code. If you can't fix your compiler, you can work 
around the problem by running 'configure' with something like the following command:

./configure CC=clang CFLAGS='-U__GNUC__ -D__GNUC__=4'

Since you already are invoking 'configure' with special options, it shouldn't be 
much trouble to add another option to work around this problem with your compiler.