Reapply "Remove configure checks for supported instruction sets"

I reverted this previously for 7.4 because of bug #78769. Relanding
it now for master, because I still believe that this change is
right, and if it causes complications, those indicate a bug elsewhere.

---

These were checking whether the instruction set is supported by
the host CPU, however they were only used to condition on whether
this instruction set is targeted at all. It would still use dynamic
dispatch (e.g. based on ifunc resolvers) to select the actual
implementation. Whether the target is guaranteed to support the
instruction set without dispatch is determined based on pre-defined
macros like __SSE2__.

This removes the configure-time builtin cpu checks to remove
confusion. Additionally this allows targeting an architecture that
is newer than the host architecture.

Author: nikic

Zend/zend_portability.h

@@ -494,21 +494,21 @@ extern "C++" {
 #endif
 
 #if (defined(__i386__) || defined(__x86_64__))
-# if PHP_HAVE_SSSE3_INSTRUCTIONS && defined(HAVE_TMMINTRIN_H)
-# define PHP_HAVE_SSSE3
+# if defined(HAVE_TMMINTRIN_H)
+#  define PHP_HAVE_SSSE3
 # endif
 
-# if PHP_HAVE_SSE4_2_INSTRUCTIONS && defined(HAVE_NMMINTRIN_H)
-# define PHP_HAVE_SSE4_2
+# if defined(HAVE_NMMINTRIN_H)
+#  define PHP_HAVE_SSE4_2
 # endif
 
 /*
  * AVX2 support was added in gcc 4.7, but AVX2 intrinsics don't work in
  * __attribute__((target("avx2"))) functions until gcc 4.9.
  */
-# if PHP_HAVE_AVX2_INSTRUCTIONS && defined(HAVE_IMMINTRIN_H) && \
+# if defined(HAVE_IMMINTRIN_H) && \
   (defined(__llvm__) || defined(__clang__) || (defined(__GNUC__) && ZEND_GCC_VERSION >= 4009))
-# define PHP_HAVE_AVX2
+#  define PHP_HAVE_AVX2
 # endif
 #endif
 

build/php.m4

@@ -2669,30 +2669,6 @@ AC_DEFUN([PHP_CHECK_BUILTIN_CPU_SUPPORTS], [
    [$have_builtin_cpu_supports], [Whether the compiler supports __builtin_cpu_supports])
 ])
 
-dnl
-dnl PHP_CHECK_CPU_SUPPORTS
-dnl
-AC_DEFUN([PHP_CHECK_CPU_SUPPORTS], [
-  AC_REQUIRE([PHP_CHECK_BUILTIN_CPU_INIT])
-  AC_REQUIRE([PHP_CHECK_BUILTIN_CPU_SUPPORTS])
-  have_ext_instructions=0
-  if test $have_builtin_cpu_supports = 1; then
-    AC_MSG_CHECKING([for $1 instructions supports])
-    AC_RUN_IFELSE([AC_LANG_SOURCE([[
-int main() {
-	return __builtin_cpu_supports("$1")? 0 : 1;
-}
-    ]])], [
-      have_ext_instructions=1
-      AC_MSG_RESULT([yes])
-    ], [
-      AC_MSG_RESULT([no])
-    ], [AC_MSG_RESULT([no])])
-  fi
-  AC_DEFINE_UNQUOTED(AS_TR_CPP([PHP_HAVE_$1_INSTRUCTIONS]),
-   [$have_ext_instructions], [Whether the compiler supports $1 instructions])
-])
-
 dnl
 dnl PHP_PATCH_CONFIG_HEADERS([FILE])
 dnl

configure.ac

@@ -499,12 +499,6 @@ PHP_CHECK_BUILTIN_CPU_INIT
 dnl Check __builtin_cpu_supports
 PHP_CHECK_BUILTIN_CPU_SUPPORTS
 
-dnl Check instructions.
-PHP_CHECK_CPU_SUPPORTS([ssse3])
-PHP_CHECK_CPU_SUPPORTS([sse4.2])
-PHP_CHECK_CPU_SUPPORTS([avx])
-PHP_CHECK_CPU_SUPPORTS([avx2])
-
 dnl Check for structure members.
 AC_CHECK_MEMBERS([struct tm.tm_gmtoff],,,[#include <time.h>])
 AC_CHECK_MEMBERS([struct stat.st_blksize, struct stat.st_rdev])