selfhost: Don't assume that the basename of the compiler is 'foo++'

Now invocations such as `g++-<version>`, `x86_64-pc-serenity-g++`, and
more will all get the g++ flags added, instead of spewing warinings
about string literals all over the console.

This also means that cross-compiling with x86_64-pc-serenity-clang++
will actually apply target flags.

selfhost/main.jakt

@@ -576,7 +576,7 @@ fn compiler_main(anon args: [String]) throws -> c_int {
     }
 
     let compiler_is = fn[cxx_compiler_path](anon name: String) throws -> bool {
-        return Path::from_string(cxx_compiler_path).basename() == name
+        return Path::from_string(cxx_compiler_path).basename().contains(name)
     }
 
     mut file_name: String? = None

selfhost/platform/posix_compiler.jakt

@@ -15,7 +15,7 @@ fn run_compiler(
     mut file_path = Path::from_string(cxx_compiler_path)
 
     mut extra_flags: [String] = []
-    if file_path.basename() == "g++" {
+    if file_path.basename().contains("g++") {
         extra_flags.push("-Wno-literal-suffix")
         extra_flags.push("-Wno-unused-parameter")
         extra_flags.push("-Wno-unused-but-set-variable")