Support -static-stdlib on non-Apple platforms (#24)

* Support `--static-stdlib` on non-Apple platforms

Fixes #23.

* CI

* wip

* wip

* wip

* wip

* give up

Author: stephencelis

Makefile

@@ -16,7 +16,19 @@ test-linux:
 		-v "$(PWD):$(PWD)" \
 		-w "$(PWD)" \
 		swift:5.6.2-focal \
-		bash -c "make test"
+		bash -c "apt-get update && apt-get install make && make test"
+
+test-linux-static-stdlib:
+	@docker run \
+		-v "$(PWD):$(PWD)" \
+		-w "$(PWD)" \
+		swift:5.6.2-focal \
+		bash -c "swift build -c debug -Xswiftc -static-stdlib"
+	@docker run \
+		-v "$(PWD):$(PWD)" \
+		-w "$(PWD)" \
+		swift:5.6.2-focal \
+		bash -c "swift build -c release -Xswiftc -static-stdlib"
 
 format:
 	@swift format \

Package.resolved

@@ -65,9 +65,12 @@
       dlsym(dlopen(nil, RTLD_LAZY), "_XCTFailureHandler"),
       to: XCTFailureHandler.self
     )
-  #else
+  #elseif canImport(XCTest)
     // NB: It seems to be safe to import XCTest on Linux
     @_exported import func XCTest.XCTFail
+  #else
+    public func XCTFail(_ message: String = "") {}
+    public func XCTFail(_ message: String = "", file: StaticString, line: UInt) {}
   #endif
 #else
   /// This function generates a failure immediately and unconditionally.