improve clang support (11)

[Bruno Haible]

clang does not have
  __builtin_add_overflow_p
  __builtin_sub_overflow_p
  __builtin_mul_overflow_p
Therefore the condition
  (7 <= __GNUC__)
used in intprops.h and xalloc-oversized.h is fine: it evaluates to false on
clang (since clang pretends to be GCC 4.2.1 compatible on Unix platforms).


2020-08-09  Bruno Haible  <bruno@clisp.org>

        intprops: Fix typo in comment.
        * lib/intprops.h (_GL_HAS_BUILTIN_OVERFLOW_P): Fix typo in comment.

diff --git a/lib/intprops.h b/lib/intprops.h
index 6de65b0..c0bfecd 100644
--- a/lib/intprops.h
+++ b/lib/intprops.h
@@ -239,7 +239,7 @@
 #endif
 
 /* True if __builtin_add_overflow_p (A, B, C) works, and similarly for
-   __builtin_mul_overflow_p and __builtin_mul_overflow_p.  */
+   __builtin_sub_overflow_p and __builtin_mul_overflow_p.  */
 #define _GL_HAS_BUILTIN_OVERFLOW_P (7 <= __GNUC__)
 
 /* The _GL*_OVERFLOW macros have the same restrictions as the