improve clang support (17)

[Bruno Haible]

clang has the __builtin_popcount{,l,ll} primitives, and they expand to
inline code (unlike the implementation in GCC), so it cannot cause a
link error.


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

        count-one-bits: Use __builtin_popcount{,l,ll} on clang.
        * lib/count-one-bits.h (COUNT_ONE_BITS): Use the GCC built-in.

diff --git a/lib/count-one-bits.h b/lib/count-one-bits.h
index 6c5b757..a9e166a 100644
--- a/lib/count-one-bits.h
+++ b/lib/count-one-bits.h
@@ -38,7 +38,8 @@ extern "C" {
    expand to code that computes the number of 1-bits 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)
+#if (__GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)) \
+    || (__clang_major__ >= 4)
 # define COUNT_ONE_BITS(GCC_BUILTIN, MSC_BUILTIN, TYPE) \
     return GCC_BUILTIN (x)
 #else