#6 cproto chokes on GNU __attribute__ syntax

[Eric Gallager]

For example, it will turn:

void *a_chooser() __asm__("_a") __attribute__((visibility("hidden"), noinline));

into:

void *a_chooser() __asm__("_a") __attribute__;

The result is no longer valid, and will lead to compile failures. See https://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html for more info.