libcutils: turn on -Werror on Win32, fix resulting build break.

Mingw doesn't provide strndup or strtok_r used in str_parms.c, resulting in
-Wimplicit-function-declaration being emitted for the Windows build.
None of the consumers of str_parms.c appear to be compiled for Windows,
so we can just remove it from the Windows build.

Change-Id: I36b66fc54ed261d38f5294bc8662ddb2db4fe64f