[ARM, sim] Fix build error and warnings

[ARM, sim] Fix build error and warnings

Newer GCC's have switched to -fno-common by default, and this breaks the build
for the ARM sim, like this:

binutils-gdb.git~gdb-8.3-release/sim/arm/maverick.c:65: multiple definition of `DSPsc'; libsim.a(wrapper.o):binutils-gdb.git~gdb-8.3-release/sim/arm/wrapper.c:134: first defined here
binutils-gdb.git~gdb-8.3-release/sim/arm/maverick.c:64: multiple definition of `DSPacc'; libsim.a(wrapper.o):binutils-gdb.git~gdb-8.3-release/sim/arm/wrapper.c:133: first defined here
binutils-gdb.git~gdb-8.3-release/sim/arm/maverick.c:63: multiple definition of `DSPregs'; libsim.a(wrapper.o):binutils-gdb.git~gdb-8.3-release/sim/arm/wrapper.c:132: first defined here

I also noticed a few warnings due to mismatching types, as follows:

../../../../repos/binutils-gdb/sim/arm/wrapper.c: In function ‘sim_create_inferior’:
../../../../repos/binutils-gdb/sim/arm/wrapper.c:335:16: warning: assignment discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
       for (arg = argv; *arg != NULL; arg++)
                ^
../../../../repos/binutils-gdb/sim/arm/wrapper.c:342:8: warning: assignment discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
    arg = argv;
        ^
../../../../repos/binutils-gdb/sim/arm/wrapper.c:345:13: warning: assignment discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
    for (arg = argv; *arg != NULL; arg++)
             ^
The following patch fixes both of the above.

sim/arm/ChangeLog:

2019-12-06  Luis Machado  <luis.machado@linaro.org>

	* armemu.c (isize): Move this declaration ...
	* arminit.c (isize): ... here.
	* maverick.h: New file.
	* wrapper.c: Include "maverick.h".
	(<struct maverick_regs>, <union maverick_acc_regs>): Remove and update
	comment.
	(sim_create_inferior): Cast variables to proper type.
	* maverick.c: Include "maverick.h".
	(<struct maverick_regs>, <union maverick_acc_regs>): Move
	declarations to maverick.h and update comment.
	(DSPsc, DSPacc, DSPregs): Adjust comment.

Change-Id: I21db699d3b61b2de8c44053e47be4387285af28f