msan_generator should specify NameMangling::C
msan_generator should specify NameMangling::C

NameMangling::Default leaves it at the mercy of what’s in the Target,
which can differ between Makefile and Bazel (the latter defaults to c++
mangling on).

Former-commit-id: af812e70396a60b9e389f61487d55c9fe92dad2b
darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide