compile: set debug compile: Display GCC driver filename

compile: set debug compile: Display GCC driver filename

As discussed in
	How to use compile & execute function in GDB
	https://sourceware.org/ml/gdb/2015-04/msg00026.html

GDB currently searches for compilers on /usr/bin/ARCH-OS-gcc and
chooses a match from there.  However, it is not currently possible for
the user to display which compiler was selected.  Up until now, GDB's
compiler interface was not up-to-date with GCC's one, which means that
it wasn't possible to obtain this information.  This patch implements
the mechanisms necessary for that.

gdb/ChangeLog
2017-08-23  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* compile/compile.c (compile_to_object): Conditionally call
	set_verbose.  Conditionally call compile or compile_v0.

include/ChangeLog
2017-08-23  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gcc-interface.h (enum gcc_base_api_version): Add
	GCC_FE_VERSION_1.
	(struct gcc_base_vtable): Rename compile to compile_v0.  Update
	comment for compile.  New methods set_verbose and compile.