Fix stub functions in MicroStdlib test.

Author: Greg Parker

validation-test/stdlib/MicroStdlib/Inputs/RuntimeStubs.c

@@ -1,12 +1,12 @@
 int $SBi32_N;
 int $SBi64_N;
 int $SBi8_N;
-void _swift_getEnumCaseSinglePayload(void) {}
-void _swift_getGenericMetadata(void) {}
-void _swift_slowAlloc(void) {}
-void _swift_slowDealloc(void) {}
-void _swift_storeEnumTagSinglePayload(void) {}
+void swift_getEnumCaseSinglePayload(void) {}
+void swift_getGenericMetadata(void) {}
+void swift_slowAlloc(void) {}
+void swift_slowDealloc(void) {}
+void swift_storeEnumTagSinglePayload(void) {}
 void swift_allocateGenericValueMetadata(void) {}
 void swift_initEnumMetadataSinglePayload(void) {}
-void _swift_retain(){}
+void swift_retain(){}
 void swift_allocBox(){}