Fixed bug #8338 (Intel CET is disabled unintentionally since PHP-8.1.0)

Intel Control Flow Enforcement Technology (CET) is enabled by default
since gcc v8.1. With CET, gcc emits following processor-specific program
property types in .note.gnu.property section:
- Indirect Branch Tracking (IBT)
- Shadow Stack (SHSTK)

Such properties are there before PHP-8.1.0.
$ sudo readelf -n sapi/cli/php
Displaying notes found in: .note.gnu.property
  Owner                Data size        Description
  GNU                  0x00000020       NT_GNU_PROPERTY_TYPE_0
        Properties: x86 feature: IBT, SHSTK
        x86 ISA needed: x86-64-baseline

However, the properties are missing since PHP-8.1.0.
$ sudo readelf -n sapi/cli/php
Displaying notes found in: .note.gnu.property
  Owner                Data size        Description
  GNU                  0x00000010       NT_GNU_PROPERTY_TYPE_0
        Properties: x86 ISA needed: x86-64-baseline

This is caused by commit c276c16 "Implement Fibers" which introduces
some assembly files such as jump_x86_64_sysv_elf_gas.S and
make_x86_64_sysv_elf_gas.S. The object files of such assembly miss
.note.gnu.property section and thus the final output files miss it too.

Fix this via adding linker option.

Signed-off-by: Chen, Hu <[email protected]>

Author: chen-hu-97

configure.ac

@@ -352,6 +352,23 @@ if test -d /usr/pkg/include -a -d /usr/pkg/lib ; then
 fi
 test -d /usr/ucblib && PHP_ADD_LIBPATH(/usr/ucblib)
 
+dnl Check whether the Intel CET is enabled
+AC_CACHE_CHECK([whether Intel CET is enabled], ac_cv_intel_cet_enabled, [
+  AC_COMPILE_IFELSE([
+    AC_LANG_SOURCE([[
+      #ifndef __CET__
+      # error CET is not enabled
+      #endif
+      ]])], [
+        ac_cv_intel_cet_enabled=yes
+      ], [
+        ac_cv_intel_cet_enabled=no
+      ])
+    if test "$ac_cv_intel_cet_enabled" = yes; then
+      EXTRA_LDFLAGS_PROGRAM="$EXTRA_LDFLAGS_PROGRAM -Wl,-zibt -Wl,-zshstk"
+    fi
+  ])
+
 dnl First, library checks.
 dnl ----------------------------------------------------------------------------