tools: patch gyp to avoid xcrun errors

Previously running ./configure with only the Xcode Command Line Tools
installed would give:

xcrun: error: unable to lookup item 'PlatformPath' from command line tools installation
xcrun: error: unable to lookup item 'PlatformPath' in SDK '/'

Co-authored-by: Ben Noordhuis <info@bnoordhuis.nl>
Fixes: nodejs#12531

PR-URL: nodejs#21520
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

tools/gyp/pylib/gyp/xcode_emulation.py

@@ -645,9 +645,10 @@ def GetCflags(self, configname, arch=None):
 
     cflags += self._Settings().get('WARNING_CFLAGS', [])
 
-    platform_root = self._XcodePlatformPath(configname)
-    if platform_root and self._IsXCTest():
-      cflags.append('-F' + platform_root + '/Developer/Library/Frameworks/')
+    if self._IsXCTest():
+        platform_root = self._XcodePlatformPath(configname)
+        if platform_root:
+          cflags.append('-F' + platform_root + '/Developer/Library/Frameworks/')
 
     if sdk_root:
       framework_root = sdk_root
@@ -913,10 +914,11 @@ def GetLdflags(self, configname, product_dir, gyp_to_build_path, arch=None):
     for directory in framework_dirs:
       ldflags.append('-F' + directory.replace('$(SDKROOT)', sdk_root))
 
-    platform_root = self._XcodePlatformPath(configname)
-    if sdk_root and platform_root and self._IsXCTest():
-      ldflags.append('-F' + platform_root + '/Developer/Library/Frameworks/')
-      ldflags.append('-framework XCTest')
+    if self._IsXCTest():
+        platform_root = self._XcodePlatformPath(configname)
+        if sdk_root and platform_root:
+          ldflags.append('-F' + platform_root + '/Developer/Library/Frameworks/')
+          ldflags.append('-framework XCTest')
 
     is_extension = self._IsIosAppExtension() or self._IsIosWatchKitExtension()
     if sdk_root and is_extension: