Patch CMake Swift module to correctly load flags

This fixes an issue with the Swift CMake module in CMake < 3.16.0 that causes default flags not to be loaded properly leading to unoptimized builds in release mode.

Author: drexin

utils/swift_build_support/swift_build_support/cmake-swift.patch

@@ -0,0 +1,25 @@
+From dbc2c645465a7045efe4d4d0a791ebbdd514343a Mon Sep 17 00:00:00 2001
+From: Dario Rexin <drexin@apple.com>
+Date: Sat, 28 Mar 2020 15:30:26 -0700
+Subject: [PATCH] Load swift flags in swift module
+
+---
+ Modules/CMakeSwiftInformation.cmake | 2 ++
+ 1 file changed, 2 insertions(+)
+
+diff --git a/Modules/CMakeSwiftInformation.cmake b/Modules/CMakeSwiftInformation.cmake
+index f6510b922f..6d3fe187a7 100644
+--- a/Modules/CMakeSwiftInformation.cmake
++++ b/Modules/CMakeSwiftInformation.cmake
+@@ -47,6 +47,8 @@ set(CMAKE_Swift_FLAGS_RELEASE_INIT "-O")
+ set(CMAKE_Swift_FLAGS_RELWITHDEBINFO_INIT "-O -g")
+ set(CMAKE_Swift_FLAGS_MINSIZEREL_INIT "-Osize")
+ 
++cmake_initialize_per_config_variable(CMAKE_Swift_FLAGS "Swift Compiler Flags")
++
+ # NOTE(compnerd) we do not have an object compile rule since we build the objects as part of the link step
+ if(NOT CMAKE_Swift_COMPILE_OBJECT)
+   set(CMAKE_Swift_COMPILE_OBJECT ":")
+-- 
+2.15.0
+

utils/swift_build_support/swift_build_support/cmake.py

@@ -235,18 +235,36 @@ def build_cmake(self, source_root, build_root):
                 if len(m) == 1:
                     build_root = m[0]
 
-        cmake_build_dir = os.path.join(build_root, 'cmake-%s' %
+        cmake_install_dir = os.path.join(build_root, 'cmake-%s' %
+                                         self.args.host_target)
+        cmake_build_dir = os.path.join(build_root, 'cmake-%s-build' %
                                        self.args.host_target)
         if not os.path.isdir(cmake_build_dir):
             os.makedirs(cmake_build_dir)
 
         cwd = os.getcwd()
+
+        file_dir = os.path.dirname(os.path.abspath(__file__))
+        cmake_patch_path = os.path.join(file_dir, "cmake-swift.patch")
+        cmake_source_dir = os.path.join(source_root, "cmake")
+        os.chdir(cmake_source_dir)
+        shell.call_without_sleeping(['git', 'apply', cmake_patch_path],
+                                    echo=True)
+
         os.chdir(cmake_build_dir)
-        shell.call_without_sleeping([cmake_bootstrap], echo=True)
+        shell.call_without_sleeping([cmake_bootstrap, '--prefix=%s' %
+                                    cmake_install_dir], echo=True)
         shell.call_without_sleeping(['make', '-j%s' % self.args.build_jobs],
                                     echo=True)
+        shell.call_without_sleeping(['make', 'install'], echo=True)
+
+        os.chdir(cmake_source_dir)
+        # undo the patch so the next time we call this it applies again
+        shell.call_without_sleeping(['git', 'checkout', '-f'],
+                                    echo=True)
+
         os.chdir(cwd)
-        return os.path.join(cmake_build_dir, 'bin', 'cmake')
+        return os.path.join(cmake_install_dir, 'bin', 'cmake')
 
     # For Linux only, determine the version of the installed CMake compared to
     # the source and build the source if necessary. Returns the path to the