[clang-scan-deps] Add -M to work around -MT issue after r371918

gcc will complain if -MT is used but neither -M nor -MM is specified:

> cc1: error: to generate dependencies you must specify either -M or -MM

r371918 changed our behavior to match GCC, but apparently
clang-scan-deps is not happy.

llvm-svn: 371920

clang/tools/clang-scan-deps/ClangScanDeps.cpp

@@ -242,6 +242,7 @@ int main(int argc, const char **argv) {
         AdjustedArgs.push_back("-o");
         AdjustedArgs.push_back("/dev/null");
         if (!HasMT && !HasMQ) {
+          AdjustedArgs.push_back("-M");
           AdjustedArgs.push_back("-MT");
           // We're interested in source dependencies of an object file.
           if (!HasMD) {