cmake: extract version string and add PrintVersion.cmake

Add a helper to allow us to programatically extract the Swift version
string during the build.  This is particularly useful for injection into
the packaging stages.

Author: compnerd

CMakeLists.txt

@@ -304,12 +304,7 @@ endif()
 set(SWIFT_ANALYZE_CODE_COVERAGE FALSE CACHE STRING
     "Build Swift with code coverage instrumenting enabled [FALSE, NOT-MERGED, MERGED]")
 
-# SWIFT_VERSION is deliberately /not/ cached so that an existing build directory
-# can be reused when a new version of Swift comes out (assuming the user hasn't
-# manually set it as part of their own CMake configuration).
-set(SWIFT_VERSION_MAJOR 5)
-set(SWIFT_VERSION_MINOR 9)
-set(SWIFT_VERSION "${SWIFT_VERSION_MAJOR}.${SWIFT_VERSION_MINOR}")
+include(cmake/SwiftVerison.cmake)
 
 set(SWIFT_VENDOR "" CACHE STRING
     "The vendor name of the Swift compiler")

cmake/PrintVersion.cmake

@@ -0,0 +1,2 @@
+include(SwiftVersion.cmake)
+message(${SWIFT_VERSION})

cmake/SwiftVersion.cmake

@@ -0,0 +1,6 @@
+# SWIFT_VERSION is deliberately /not/ cached so that an existing build directory
+# can be reused when a new version of Swift comes out (assuming the user hasn't
+# manually set it as part of their own CMake configuration).
+set(SWIFT_VERSION_MAJOR 5)
+set(SWIFT_VERSION_MINOR 9)
+set(SWIFT_VERSION "${SWIFT_VERSION_MAJOR}.${SWIFT_VERSION_MINOR}")