Fix #76825: Undefined symbols ___cpuid_count

Apparently, the presence of `cpuid.h` is not necessarily sufficient to
guarantee the availability of `__cpuid_count()`.  We therefore test for
the latter explicitly.

Author: cmb69

NEWS

@@ -3,6 +3,7 @@ PHP                                                                        NEWS
 ?? ??? ????, PHP 7.3.0RC5
 
 - Core:
+  . Fixed bug #76825 (Undefined symbols ___cpuid_count). (Laruence, cmb)
   . Fixed bug #77110 (undefined symbol zend_string_equal_val in C++ build).
     (Remi)
 
@@ -139,7 +140,6 @@ PHP                                                                        NEWS
 13 Sep 2018, PHP 7.3.0RC1
 
 - Core:
-  . Fixed bug #76825 (Undefined symbols ___cpuid_count). (Laruence)
   . Fixed bug #76820 (Z_COPYABLE invalid definition). (mvdwerve, cmb)
   . Fixed bug #76510 (file_exists() stopped working for phar://). (cmb)
 

Zend/Zend.m4

@@ -596,3 +596,21 @@ dnl This is the most probable fallback so we assume yes in case of cross compile
 if test "$ac_cv_huge_val_nan" = "yes"; then
   AC_DEFINE([HAVE_HUGE_VAL_NAN], 1, [whether HUGE_VAL + -HUGEVAL == NAN])
 fi
+
+dnl
+dnl Check whether __cpuid_count is available
+dnl
+AC_CACHE_CHECK(whether __cpuid_count is available, ac_cv_cpuid_count_available, [
+AC_LINK_IFELSE([AC_LANG_PROGRAM([[
+  #include <cpuid.h>
+]], [[
+  unsigned eax, ebx, ecx, edx;
+  __cpuid_count(0, 0, eax, ebx, ecx, edx);
+]])], [
+  ac_cv_cpuid_count_available=yes
+], [
+  ac_cv_cpuid_count_available=no
+])])
+if test "$ac_cv_cpuid_count_available" = "yes"; then
+  AC_DEFINE([HAVE_CPUID_COUNT], 1, [whether __cpuid_count is available])
+fi

Zend/zend_cpuinfo.c

@@ -29,7 +29,7 @@ typedef struct _zend_cpu_info {
 static zend_cpu_info cpuinfo = {0};
 
 #if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
-# ifdef HAVE_CPUID_H
+# if defined(HAVE_CPUID_H) && defined(HAVE_CPUID_COUNT)
 # include <cpuid.h>
 static void __zend_cpuid(uint32_t func, uint32_t subfunc, zend_cpu_info *cpuinfo) {
 	__cpuid_count(func, subfunc, cpuinfo->eax, cpuinfo->ebx, cpuinfo->ecx, cpuinfo->edx);