Fix the C-API MCJIT test for 32-bit big endian machines.

Fix the C-API MCJIT test for 32-bit big endian machines.

Avoid using unions for storing the return value from
LLVMGetGlobalValueAddress() and LLVMGetFunctionAddress() and accessing it as
a pointer through another pointer member. This causes problems on 32-bit big
endian machines since the pointer gets the higher part of the return value of
the aforementioned functions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226170 91177308-0d34-0410-b5e6-96231b3b80d8