x86: Add support to build strcmp/strlen/strchr with explicit ISA level

1. Add default ISA level selection in non-multiarch/rtld
   implementations.

2. Add ISA level build guards to different implementations.
    - I.e strcmp-avx2.S which is ISA level 3 will only build if
      compiled ISA level <= 3. Otherwise there is no reason to
      include it as we will always use one of the ISA level 4
      implementations (strcmp-evex.S).

3. Refactor the ifunc selector and ifunc implementation list to use
   the ISA level aware wrapper macros that allow functions below the
   compiled ISA level (with a guranteed replacement) to be skipped.

Tested with and without multiarch on x86_64 for ISA levels:
{generic, x86-64-v2, x86-64-v3, x86-64-v4}

And m32 with and without multiarch.

1 files changed, 6 insertions, 1 deletions

diff --git a/sysdeps/x86_64/multiarch/wcsnlen-sse4_1.S b/sysdeps/x86_64/multiarch/wcsnlen-sse4_1.S
index 17cdedc2a9..8f534102a2 100644
--- a/sysdeps/x86_64/multiarch/wcsnlen-sse4_1.S
+++ b/sysdeps/x86_64/multiarch/wcsnlen-sse4_1.S
@@ -1,6 +1,11 @@
+#ifndef WCSNLEN
+# define WCSNLEN	__wcsnlen_sse4_1
+# define OVERFLOW_STRLEN	__wcslen_sse4_1
+#endif
+
 #define AS_WCSLEN
 #define AS_STRNLEN
-#define STRLEN	__wcsnlen_sse4_1
+#define STRLEN	WCSNLEN
 #define SECTION(p)	p##.sse4.1
 
 #include "strlen-sse2.S"