test: do not link against libcmt on Win32

Since we do not support building in `/MT` or `/MTd` mode currently,
ensure that we link against the dynamic runtime.  This allows us to
properly run tests without getting lucky in the internal structures
of libc aligning up across the variants.

Author: compnerd

test/lit.cfg

@@ -804,12 +804,10 @@ elif run_os in ['windows-msvc']:
     config.target_runtime = 'native'
 
     config.target_build_swift =                                                  \
-            ('%r -target %s %s %s %s %s' % (config.swiftc,                       \
-                                            config.variant_triple,               \
-                                            resource_dir_opt,                    \
-                                            config.swift_test_options,           \
-                                            config.swift_driver_test_options,    \
-                                            swift_execution_tests_extra_flags))
+            ('%r -target %s %s %s %s %s -Xlinker -nodefaultlib:libcmt' %         \
+                    (config.swiftc, config.variant_triple, resource_dir_opt,     \
+                     config.swift_test_options, config.swift_driver_test_options,\
+                     swift_execution_tests_extra_flags))
 
     config.target_run = ''