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, 10 insertions, 4 deletions

diff --git a/sysdeps/x86_64/multiarch/wcscmp-sse2.S b/sysdeps/x86_64/multiarch/wcscmp-sse2.S
index 6cb7d9faf9..3f32e8127d 100644
--- a/sysdeps/x86_64/multiarch/wcscmp-sse2.S
+++ b/sysdeps/x86_64/multiarch/wcscmp-sse2.S
@@ -16,11 +16,16 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#define USE_AS_WCSCMP
-#define STRCMP_ISA	_sse2
-#include "strcmp-naming.h"
+#include <isa-level.h>
 
-#include <sysdep.h>
+/* ISA level >= 2 because there is no wcscmp-sse4 implementations.  */
+#if ISA_SHOULD_BUILD (2)
+# include <sysdep.h>
+
+/* Needed to get right name.  */
+# define USE_AS_WCSCMP
+# define STRCMP_ISA	_sse2
+# include "strcmp-naming.h"
 
 /* Note: wcscmp uses signed comparison, not unsighed as in strcmp function. */
 
@@ -949,3 +954,4 @@ L(equal):
 	ret
 
 END (STRCMP)
+#endif