[wasm][test] Force static library to avoid unsupported shared library build

Linking libraries without `-static` flag produces unexpected main
function reference error. This is because the linker is trying to link
input objects as executable, not as library.

Author: kateinoigakukun

test/lit.cfg

@@ -1837,7 +1837,7 @@ elif run_os == 'wasi':
         config.swift_driver_test_options, swift_execution_tests_extra_flags])
     config.target_codesign = "echo"
     config.target_build_swift_dylib = (
-        "%s -parse-as-library -emit-library -o '\\1'"
+        "%s -parse-as-library -emit-library -static -o '\\1'"
         % (config.target_build_swift))
     config.target_add_rpath = ''
     config.target_swift_frontend = ' '.join([