[HIP] Do not emit debug info for stub function

The stub function is generated by compiler and its instructions have nothing
to do with the kernel source code.

Currently clang generates debug info for the stub function, which causes
confusion for the HIP debugger. For example, when users set break point
on a line of a kernel, the debugger should break on that line when the kernel is
executed and reaches that line, but instead the debugger breaks in the stub function.

This patch disables debug info for stub function for HIP.

Differential Revision: https://reviews.llvm.org/D79866