[cmake] Add an option to enable/disable creation of "sib" stdlib targets and disable it by default.

These aren't really being used and generating these cause unnecessary configure
time in cmake.

Author: gottesmm

CMakeLists.txt

@@ -195,6 +195,10 @@ option(SWIFT_ENABLE_PARSEABLE_MODULE_INTERFACES
        "Generate .swiftinterface files alongside .swiftmodule files"
        TRUE)
 
+option(SWIFT_STDLIB_ENABLE_SIB_TARGETS
+       "Should we generate sib targets for the stdlib or not?"
+       FALSE)
+
 #
 # User-configurable Android specific options.
 #

stdlib/CMakeLists.txt

@@ -102,9 +102,11 @@ function(swift_create_stdlib_targets name variant define_all_alias)
 endfunction()
 
 swift_create_stdlib_targets("swift-stdlib" "" TRUE)
-swift_create_stdlib_targets("swift-stdlib" "sib" TRUE)
-swift_create_stdlib_targets("swift-stdlib" "sibopt" TRUE)
-swift_create_stdlib_targets("swift-stdlib" "sibgen" TRUE)
+if(SWIFT_STDLIB_ENABLE_SIB_TARGETS)
+  swift_create_stdlib_targets("swift-stdlib" "sib" TRUE)
+  swift_create_stdlib_targets("swift-stdlib" "sibopt" TRUE)
+  swift_create_stdlib_targets("swift-stdlib" "sibgen" TRUE)
+endif()
 swift_create_stdlib_targets("swift-test-stdlib" "" FALSE)
 
 foreach(sdk ${SWIFT_SDKS})