Use PKG_CHECK_MODULES to detect the ffi library

ext/ffi/config.m4

@@ -6,47 +6,17 @@ PHP_ARG_WITH([ffi],
     [Include FFI support])])
 
 if test "$PHP_FFI" != "no"; then
-  if test -r $PHP_FFI/include/ffi.h; then
-    FFI_INCDIR=$PHP_FFI/include
-    FFI_LIBDIR=$PHP_FFI
-  else
-    if test -x "$PKG_CONFIG" && "$PKG_CONFIG" --exists libffi; then
-      FFI_VER=`"$PKG_CONFIG" --modversion libffi`
-      FFI_INCDIR=`"$PKG_CONFIG" --variable=includedir libffi`
-      FFI_LIBDIR=`"$PKG_CONFIG" --variable=libdir libffi`
-      AC_MSG_CHECKING(for libffi)
-      AC_MSG_RESULT(found version $FFI_VER)
-    else
-      AC_MSG_CHECKING(for libffi in default path)
-      for i in /usr/local /usr; do
-        if test -r $i/include/ffi.h; then
-          FFI_DIR=$i
-          AC_MSG_RESULT(found in $i)
-          break
-        fi
-      done
-
-      if test -z "$FFI_DIR"; then
-        AC_MSG_RESULT(not found)
-        AC_MSG_ERROR(Please reinstall the libffi distribution)
-      fi
-
-      FFI_INCDIR="$FFI_DIR/include"
-      FFI_LIBDIR="$FFI_DIR/$PHP_LIBDIR"
-    fi
-  fi
+  PKG_CHECK_MODULES([FFI], [libffi])
 
   AC_CHECK_TYPES(long double)
 
   PHP_CHECK_LIBRARY(ffi, ffi_call,
   [
-    PHP_ADD_INCLUDE($FFI_INCDIR)
-    PHP_ADD_LIBRARY_WITH_PATH(ffi, $FFI_LIBDIR, FFI_SHARED_LIBADD)
+    PHP_EVAL_INCLINE($FFI_CFLAGS)
+    PHP_EVAL_LIBLINE($FFI_LIBS, FFI_SHARED_LIBADD)
     AC_DEFINE(HAVE_FFI,1,[ Have ffi support ])
   ], [
     AC_MSG_ERROR(FFI module requires libffi)
-  ], [
-    -L$FFI_LIBDIR
   ])
 
   PHP_NEW_EXTENSION(ffi, ffi.c ffi_parser.c, $ext_shared,, -DZEND_ENABLE_STATIC_TSRMLS_CACHE=1)