8251858: Update to Xcode 11.3.1

Reviewed-by: jvos, arapte

build.properties

@@ -90,7 +90,7 @@ jfx.gradle.version.min=5.3
 # Toolchains
 jfx.build.linux.gcc.version=gcc9.2.0-OL6.4+1.0
 jfx.build.windows.msvc.version=VS2019-16.5.3+1.0
-jfx.build.macosx.xcode.version=Xcode10.1-MacOSX10.14+1.0
+jfx.build.macosx.xcode.version=Xcode11.3.1-MacOSX10.15+1.0
 
 # Build tools
 jfx.build.cmake.version=3.13.3

buildSrc/mac.gradle

@@ -45,7 +45,7 @@ MAC.libDest = "lib"
  * In extreme cases you can provide your own properties in your home dir to
  * override these settings or pass them on the command line.
  */
-def prefSdkVersion = "10.11"
+def prefSdkVersion = "10.15"
 def defaultSdkPath = "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX${prefSdkVersion}.sdk";
 
 // Set the minimum API version that we require (developers do not need to override this)