Re: improve clang support (1)

[Paul Eggert]

On 8/5/20 10:32 AM, Bruno Haible wrote:
> clang has __builtin_clz, __builtin_clzl, __builtin_clzll, also on Windows.
> At least in versions >= 4.0.0.

Should this sort of thing be using __has_builtin if available? Something like 
the following untested patch for count-leading-zeros.h (this is inspired by how 
verify.h does it):

diff --git a/lib/count-leading-zeros.h b/lib/count-leading-zeros.h
index 7cf605a5f..622c22be2 100644
--- a/lib/count-leading-zeros.h
+++ b/lib/count-leading-zeros.h
@@ -34,12 +34,22 @@ _GL_INLINE_HEADER_BEGIN
 extern "C" {
 #endif

+/* Whether __builtin_clz etc. work.  */
+#if 3 < __GNUC__ + (4 <= __GNUC_MINOR__)
+# define _GL_HAS_BUILTIN_CLZ 1
+#elif defined __has_builtin
+# define _GL_HAS_BUILTIN_CLZ (__has_builtin (__builtin_clz) \
+                              && __has_builtin (__builtin_clzl) \
+                              && __has_builtin (__builtin_clzll))
+#else
+# define _GL_HAS_BUILTIN_CLZ 0
+#endif
+
 /* Assuming the GCC builtin is BUILTIN and the MSC builtin is MSC_BUILTIN,
    expand to code that computes the number of leading zeros of the local
    variable 'x' of type TYPE (an unsigned integer type) and return it
    from the current function.  */
-#if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4) \
-    || (__clang_major__ >= 4)
+#if _GL_HAS_BUILTIN_CLZ
 # define COUNT_LEADING_ZEROS(BUILTIN, MSC_BUILTIN, TYPE)                \
   return x ? BUILTIN (x) : CHAR_BIT * sizeof x;
 #elif _MSC_VER