[compiler-rt/profile] Include __llvm_profile_get_magic in module signature

The INSTR_PROF_RAW_MAGIC_* number in profraw files should match during
profile merging.  This causes an error with 32-bit and 64-bit variants
of the same code.  The module signatures for the two binaries are
identical but they use different INSTR_PROF_RAW_MAGIC_* causing a
failure when profile-merging is used.  Including it when computing the
module signature yields different signatures for the 32-bit and 64-bit
profiles.

Differential Revision: https://reviews.llvm.org/D114054