Disable the clang/llvm optimizer for a method that triggers wrong codegen.

Disable the clang/llvm optimizer for a method that triggers wrong codegen.

There is a bug in the clang-3.5 optimizer. The issue is that in release
build the optimizer is mistyping (or just wrongly decides to use 32 bit
operation for a corner case of MIN_LONG) the args of the (ltemp / lval2)
to int (it does a 32 bit div operation instead of 64 bit.)
For the case of lval1 and lval2 equal to MIN_LONG (0x8000000000000000)
this results in raising a SIGFPE.

Commit migrated from https://github.com/dotnet/coreclr/commit/93a90d45e66eefe916295f2812a3c6437b0806b3