Replace uses of exec_program with execute_process

As of CMake 3.28, uses of exec_program produce a deprecation warning
suggesting to replace it with execute_process.

See https://cmake.org/cmake/help/latest/policy/CMP0153.html

cmake/OptimizeForArchitecture.cmake

@@ -70,7 +70,7 @@ macro(AutodetectHostArchitecture)
       string(REGEX REPLACE ".*model[ \t]*:[ \t]+([a-zA-Z0-9_-]+).*" "\\1" _cpu_model "${_cpuinfo}")
       string(REGEX REPLACE ".*flags[ \t]*:[ \t]+([^\n]+).*" "\\1" _cpu_flags "${_cpuinfo}")
    elseif(CMAKE_SYSTEM_NAME STREQUAL "Darwin")
-      exec_program("/usr/sbin/sysctl -n machdep.cpu.vendor machdep.cpu.model machdep.cpu.family machdep.cpu.features" OUTPUT_VARIABLE _sysctl_output_string)
+      execute_process(COMMAND /usr/sbin/sysctl -n machdep.cpu.vendor machdep.cpu.model machdep.cpu.family machdep.cpu.features OUTPUT_STRIP_TRAILING_WHITESPACE OUTPUT_VARIABLE _sysctl_output_string)
       string(REPLACE "\n" ";" _sysctl_output ${_sysctl_output_string})
       list(GET _sysctl_output 0 _vendor_id)
       list(GET _sysctl_output 1 _cpu_model)

cmake/VcMacros.cmake

@@ -49,7 +49,7 @@ macro(vc_determine_compiler)
       set(Vc_COMPILER_IS_GCC false)
       if(CMAKE_CXX_COMPILER MATCHES "/(icpc|icc)$")
          set(Vc_COMPILER_IS_INTEL true)
-         exec_program(${CMAKE_CXX_COMPILER} ARGS -dumpversion OUTPUT_VARIABLE Vc_ICC_VERSION)
+         execute_process(COMMAND ${CMAKE_CXX_COMPILER} -dumpversion OUTPUT_STRIP_TRAILING_WHITESPACE OUTPUT_VARIABLE Vc_ICC_VERSION)
          message(STATUS "Detected Compiler: Intel ${Vc_ICC_VERSION}")
 
          # break build with too old ICC as early as possible.
@@ -61,7 +61,7 @@ macro(vc_determine_compiler)
          message(STATUS "Detected Compiler: Open64")
       elseif(CMAKE_CXX_COMPILER MATCHES "clang\\+\\+$" OR "${_cxx_compiler_version}" MATCHES "clang")
          set(Vc_COMPILER_IS_CLANG true)
-         exec_program(${CMAKE_CXX_COMPILER} ARGS --version OUTPUT_VARIABLE Vc_CLANG_VERSION)
+         execute_process(COMMAND ${CMAKE_CXX_COMPILER} --version OUTPUT_STRIP_TRAILING_WHITESPACE OUTPUT_VARIABLE Vc_CLANG_VERSION)
          string(REGEX MATCH "[0-9]+\\.[0-9]+(\\.[0-9]+)?" Vc_CLANG_VERSION "${Vc_CLANG_VERSION}")
          message(STATUS "Detected Compiler: Clang ${Vc_CLANG_VERSION}")
 
@@ -74,13 +74,13 @@ macro(vc_determine_compiler)
          message(STATUS "Detected Compiler: MSVC ${MSVC_VERSION}")
       elseif(CMAKE_COMPILER_IS_GNUCXX)
          set(Vc_COMPILER_IS_GCC true)
-         exec_program(${CMAKE_CXX_COMPILER} ARGS -dumpversion OUTPUT_VARIABLE Vc_GCC_VERSION)
+         execute_process(COMMAND ${CMAKE_CXX_COMPILER} -dumpversion OUTPUT_STRIP_TRAILING_WHITESPACE OUTPUT_VARIABLE Vc_GCC_VERSION)
          message(STATUS "Detected Compiler: GCC ${Vc_GCC_VERSION}")
 
          # some distributions patch their GCC to return nothing or only major and minor version on -dumpversion.
          # In that case we must extract the version number from --version.
          if(NOT Vc_GCC_VERSION OR Vc_GCC_VERSION MATCHES "^[0-9]\\.[0-9]+$")
-            exec_program(${CMAKE_CXX_COMPILER} ARGS --version OUTPUT_VARIABLE Vc_GCC_VERSION)
+            execute_process(COMMAND ${CMAKE_CXX_COMPILER} --version OUTPUT_STRIP_TRAILING_WHITESPACE OUTPUT_VARIABLE Vc_GCC_VERSION)
             string(REGEX MATCH "[0-9]+\\.[0-9]+\\.[0-9]+" Vc_GCC_VERSION "${Vc_GCC_VERSION}")
             message(STATUS "GCC Version from --version: ${Vc_GCC_VERSION}")
          endif()
@@ -144,12 +144,12 @@ macro(vc_add_compiler_flag VAR _flag)
 endmacro()
 
 macro(vc_check_assembler)
-   exec_program(${CMAKE_CXX_COMPILER} ARGS -print-prog-name=as OUTPUT_VARIABLE _as)
+   execute_process(COMMAND ${CMAKE_CXX_COMPILER} -print-prog-name=as OUTPUT_STRIP_TRAILING_WHITESPACE OUTPUT_VARIABLE _as)
    mark_as_advanced(_as)
    if(NOT _as)
       message(WARNING "Could not find 'as', the assembler used by GCC. Hoping everything will work out...")
    else()
-      exec_program(${_as} ARGS --version OUTPUT_VARIABLE _as_version)
+      execute_process(COMMAND ${_as} --version OUTPUT_STRIP_TRAILING_WHITESPACE OUTPUT_VARIABLE _as_version)
       string(REGEX REPLACE "\\([^\\)]*\\)" "" _as_version "${_as_version}")
       string(REGEX MATCH "[1-9]\\.[0-9]+(\\.[0-9]+)?" _as_version "${_as_version}")
       if(_as_version VERSION_LESS "2.18.93")