Update %target-build-swift-dylib regex to handle backslashes

Supports Windows-style paths

Author: ramonasuncion

test/lit.cfg

@@ -2938,7 +2938,7 @@ config.substitutions.append(('%target-run-stdlib-swift', config.target_run_stdli
 config.substitutions.append(('%target-repl-run-simple-swift', subst_target_repl_run_simple_swift))
 config.substitutions.append(('%target-run', config.target_run))
 config.substitutions.append(('%target-jit-run', subst_target_jit_run))
-config.substitutions.append(('%target-build-swift-dylib\(([^)]+?)([^/()]+)\)', config.target_build_swift_dylib))
+config.substitutions.append(('%target-build-swift-dylib\(([^)]+?)([^/\\()]+)\)', config.target_build_swift_dylib))
 config.substitutions.append(('%target-codesign', config.target_codesign))
 config.substitutions.append(('%target-build-swift', config.target_build_swift))
 config.substitutions.append(('%target-clang', config.target_clang))