Set Swift clang-linker path

The swift driver is picking up the system clang instead of using the
clang set in `CC`. The system clang is attempting to use bfd to link
Swift, which doesn't work due to Swift's protected symbol usage.
Set the swift-driver tool directory based on the location of the clang
in use to ensure that we're picking up a consistent set of tools across
all of the tests.

Author: etcwilde

lldb/packages/Python/lldbsuite/test/make/Makefile.rules

@@ -616,6 +616,7 @@ ifeq "$(USESWIFTDRIVER)" "1"
 	ifeq "$(OS)" "Darwin"
 		SWIFTFLAGS += -sdk "$(SWIFTSDKROOT)"
 	endif
+	SWIFTFLAGS += -tools-directory "$(shell dirname $(CC))"
 endif
 
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