Cherry-pick r246309: [mips] Remove incorrect DebugLoc entries from prologue

This has been causing the prologue_end to be incorrectly positioned.

Patch by Vladimir Radosavljevic.

Differential Revision: http://reviews.llvm.org/D11293

BUG= gdb_print_symbol and gdb_stack_trace tests fail on MIPS HW
R=mseaborn@chromium.org

Review URL: https://codereview.chromium.org/2476933003 .
5 files changed