Fix g++-4.4.0 warning, it was causing llvm-nm to fail on wrapped BC files:

Path.cpp:59: warning: case label value exceeds maximum value for type
magic[0] is a (signed) char, but some case values are unsigned (e.g. 0xde).
When magic[0] was 0xde, the switch has taken the default branch instead of case
0xde branch.
Apparently this was the behaviour with older versions of gcc too, but not with g++.
Now g++-4.4 behaves as gcc, and ignores unsigned case values out of range signed
range.

llvm-svn: 70038