[build] Enable ccache for Xcode iOS builds

CMakeLists.txt

@@ -1,6 +1,26 @@
 cmake_minimum_required(VERSION 3.10 FATAL_ERROR)
 project("Mapbox GL Native" LANGUAGES CXX C)
 
+find_program(CCACHE_PROGRAM ccache)
+if(CCACHE_PROGRAM AND CMAKE_SYSTEM_NAME STREQUAL "iOS")
+    # Set up wrapper scripts
+    set(C_LAUNCHER "${CCACHE_PROGRAM}")
+    set(CXX_LAUNCHER "${CCACHE_PROGRAM}")
+    configure_file(${PROJECT_SOURCE_DIR}/scripts/ci/ccache-c.in ccache-c)
+    configure_file(${PROJECT_SOURCE_DIR}/scripts/ci/ccache-cxx.in ccache-cxx)
+    execute_process(
+        COMMAND
+            chmod
+            a+rx
+            "${CMAKE_BINARY_DIR}/ccache-c"
+            "${CMAKE_BINARY_DIR}/ccache-cxx"
+    )
+
+    # Set Xcode project attributes to route compilation and linking through our scripts
+    set(CMAKE_XCODE_ATTRIBUTE_CC "${CMAKE_BINARY_DIR}/ccache-c")
+    set(CMAKE_XCODE_ATTRIBUTE_CXX "${CMAKE_BINARY_DIR}/ccache-cxx")
+endif()
+
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 set_property(GLOBAL PROPERTY PREDEFINED_TARGETS_FOLDER Core)
 

scripts/ci/ccache-c.in

@@ -0,0 +1,9 @@
+#!/bin/sh
+
+# Xcode generator doesn't include the compiler as the
+# first argument, Ninja and Makefiles do. Handle both cases.
+if [[ "$1" = "${CMAKE_C_COMPILER}" ]] ; then
+    shift
+fi
+
+exec "${C_LAUNCHER}" "${CMAKE_C_COMPILER}" "$@"

scripts/ci/ccache-cxx.in

@@ -0,0 +1,9 @@
+#!/bin/sh
+
+# Xcode generator doesn't include the compiler as the
+# first argument, Ninja and Makefiles do. Handle both cases.
+if [[ "$1" = "${CMAKE_CXX_COMPILER}" ]] ; then
+    shift
+fi
+
+exec "${CXX_LAUNCHER}" "${CMAKE_CXX_COMPILER}" "$@"