ext/intl: level up c++ runtime std for icu 74 and onwards.

to align with what is required to build icu 74 itself.

Author: devnexen

ext/intl/config.m4

@@ -80,7 +80,28 @@ if test "$PHP_INTL" != "no"; then
     breakiterator/codepointiterator_methods.cpp"
 
   PHP_REQUIRE_CXX()
-  PHP_CXX_COMPILE_STDCXX(11, mandatory, PHP_INTL_STDCXX)
+
+  AC_MSG_CHECKING([c++ std support level])
+  AC_RUN_IFELSE([AC_LANG_SOURCE([[
+#include <unicode/uvernum.h>
+
+int main(int argc, char *argv[])
+{
+#if U_ICU_VERSION_MAJOR_NUM >= 74
+    return 0;
+#else
+    return 1;
+#endif
+}
+  ]])],[
+    AC_MSG_RESULT([c++17])
+    PHP_CXX_COMPILE_STDCXX(17, mandatory, PHP_INTL_STDCXX)
+  ],[
+    AC_MSG_RESULT([c++11])
+    PHP_CXX_COMPILE_STDCXX(11, mandatory, PHP_INTL_STDCXX)
+  ], [
+  ])
+
   PHP_INTL_CXX_FLAGS="$INTL_COMMON_FLAGS $PHP_INTL_STDCXX $ICU_CXXFLAGS"
   case $host_alias in
   *cygwin*) PHP_INTL_CXX_FLAGS="$PHP_INTL_CXX_FLAGS -D_POSIX_C_SOURCE=200809L"