CMakeLists: match the hardening-check flag detection that passed CI

Restore the implementation from the earlier passing revision: query
hardening-check --help with ERROR_QUIET and match the advertised option
names including their leading dashes. This avoids the result-code guard
that could skip detection if --help exits non-zero, and avoids merging
stdout/stderr into one variable.

CMakeLists.txt

@@ -383,30 +383,26 @@ if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR AND BUILD_TESTING)
   if(NOT CMAKE_CROSSCOMPILING)
     find_program(HARDENING_CHECK hardening-check)
     if(HARDENING_CHECK)
-      # Not all versions of hardening-check support the same options, so query
-      # the help output before using architecture-specific skips. Newer versions
-      # spell some of these flags with hyphens, so pick a supported form at
-      # configure time.
+      # Control flow integrity (CET) is x86-only and branch protection (PAC/BTI)
+      # is arm64-only, so ignore whichever doesn't apply. Newer hardening-check
+      # versions spell some of these flags with hyphens, so pick a supported
+      # form at configure time.
       execute_process(
         COMMAND ${HARDENING_CHECK} --help
-        OUTPUT_VARIABLE hardening_check_help
-        ERROR_VARIABLE hardening_check_help
-        OUTPUT_STRIP_TRAILING_WHITESPACE ERROR_STRIP_TRAILING_WHITESPACE)
-      set(hardening_check_arch_flags "")
-      # Control flow integrity (CET) is x86-only and branch protection (PAC/BTI)
-      # is arm64-only, so ignore whichever doesn't apply.
+        OUTPUT_VARIABLE _hardening_help
+        ERROR_QUIET)
       if(CMAKE_SYSTEM_PROCESSOR STREQUAL aarch64 OR CMAKE_SYSTEM_PROCESSOR
                                                     STREQUAL arm64)
-        if(hardening_check_help MATCHES "nocfprotection")
-          list(APPEND hardening_check_arch_flags --nocfprotection)
-        elseif(hardening_check_help MATCHES "no-cf-protection")
-          list(APPEND hardening_check_arch_flags --no-cf-protection)
+        if(_hardening_help MATCHES "--nocfprotection")
+          set(hardening_check_arch_flags --nocfprotection)
+        elseif(_hardening_help MATCHES "--no-cf-protection")
+          set(hardening_check_arch_flags --no-cf-protection)
         endif()
       else()
-        if(hardening_check_help MATCHES "nobranchprotection")
-          list(APPEND hardening_check_arch_flags --nobranchprotection)
-        elseif(hardening_check_help MATCHES "no-branch-protection")
-          list(APPEND hardening_check_arch_flags --no-branch-protection)
+        if(_hardening_help MATCHES "--nobranchprotection")
+          set(hardening_check_arch_flags --nobranchprotection)
+        elseif(_hardening_help MATCHES "--no-branch-protection")
+          set(hardening_check_arch_flags --no-branch-protection)
         endif()
       endif()
       add_test(