build: improve static library generation

Modern `ar` implementations support constructing the index table on the
construction.  This means that we dont need to re-read the contents and run a
second program after the initial library construction to get current behaviour.
This is a simplification of the generated build rules which improves performance
since the data is not re-read nor a second tool invoked.

Author: compnerd

CMakeLists.txt

@@ -303,6 +303,19 @@ option(SWIFT_BUILD_SOURCEKIT
     "Build SourceKit"
     ${SWIFT_BUILD_SOURCEKIT_default})
 
+#
+# Assume a new enough ar to generate the index at construction time.  This avois
+# having to invoke ranlib as a secondary command.
+#
+
+set(CMAKE_C_ARCHIVE_CREATE "<CMAKE_AR> crs <TARGET> <LINK_FLAGS> <OBJECTS>")
+set(CMAKE_C_ARCHIVE_APPEND "<CMAKE_AR> qs <TARGET> <LINK_FLAGS> <OBJECTS>")
+set(CMAKE_C_ARCHIVE_FINISH "")
+
+set(CMAKE_CXX_ARCHIVE_CREATE "<CMAKE_AR> crs <TARGET> <LINK_FLAGS> <OBJECTS>")
+set(CMAKE_CXX_ARCHIVE_APPEND "<CMAKE_AR> qs <TARGET> <LINK_FLAGS> <OBJECTS>")
+set(CMAKE_CXX_ARCHIVE_FINISH "")
+
 #
 # Include CMake modules
 #