Fix GH-8142: CYGWIN build.

pcntl: SIGPOLL/si_band unsupported.
int ext: enables the signal apis with `_POSIX_C_SOURCE`.

Author: devnexen

ext/intl/config.m4

@@ -84,7 +84,7 @@ if test "$PHP_INTL" != "no"; then
 
   PHP_REQUIRE_CXX()
   PHP_CXX_COMPILE_STDCXX(11, mandatory, PHP_INTL_STDCXX)
-  PHP_INTL_CXX_FLAGS="$INTL_COMMON_FLAGS $PHP_INTL_STDCXX $ICU_CXXFLAGS"
+  PHP_INTL_CXX_FLAGS="$INTL_COMMON_FLAGS $PHP_INTL_STDCXX $ICU_CXXFLAGS -D_POSIX_C_SOURCE=200809L"
   if test "$ext_shared" = "no"; then
     PHP_ADD_SOURCES(PHP_EXT_DIR(intl), $PHP_INTL_CXX_SOURCES, $PHP_INTL_CXX_FLAGS)
   else

ext/pcntl/pcntl.c

@@ -1160,7 +1160,7 @@ static void pcntl_siginfo_to_zval(int signo, siginfo_t *siginfo, zval *user_sigi
 			case SIGBUS:
 				add_assoc_double_ex(user_siginfo, "addr", sizeof("addr")-1, (zend_long)siginfo->si_addr);
 				break;
-#ifdef SIGPOLL
+#if defined(SIGPOLL) && !defined(__CYGWIN__)
 			case SIGPOLL:
 				add_assoc_long_ex(user_siginfo, "band", sizeof("band")-1, siginfo->si_band);
 # ifdef si_fd