gdb: Add maint set ignore-prologue-end-flag

gdb: Add maint set ignore-prologue-end-flag

The previous patch added support for the DWARF prologue-end flag in line
table. This flag can be used by DWARF producers to indicate where to
place breakpoints past a function prologue.  However, this takes
precedence over prologue analyzers. So if we have to debug a program
with erroneous debug information, the overall debugging experience will
be degraded.

This commit proposes to add a maintenance command to instruct GDB to
ignore the prologue_end flag.

Tested on x86_64-gnu-linux.

Change-Id: Idda6d1b96ba887f4af555b43d9923261b9cc6f82