* gdbarch.sh (REGISTER_NAME): Change return type a constant string

* gdbarch.sh (REGISTER_NAME): Change return type a constant string
pointer.
* gdbarch.h, gdbarch.c: Regenerate.
* config/mips/tm-mips.h (mips_register_name): Update.
* i386-tdep.h (i386_register_name): Update.
* mips-tdep.c (mips_register_name): Update
* alpha-tdep.c (alpha_register_name): Update.
* arch-utils.c (legacy_register_name): Update.
* arch-utils.h (legacy_register_name): Update.
* avr-tdep.c (avr_register_name): Update.
* ia64-tdep.c (ia64_register_name): Update.
* i386-tdep.c (i386_register_name): Update.
* sparc-tdep.c (sparc32_register_name): Update.
(sparc64_register_name): Update.
(sparclite_register_name): Update.
(sparclet_register_name):
* sh-tdep.c (sh_generic_register_name): Update.
(sh_sh_register_name): Update.
(sh_sh3_register_name): Update.
(sh_sh3e_register_name): Update.
(sh_sh_dsp_register_name): Update.
(sh_sh3_dsp_register_name): Update.
(sh_sh4_register_name): Update.
(sh_sh64_register_name): Update.
* s390-tdep.c (s390_register_name): Update.
* rs6000-tdep.c (rs6000_register_name): Update.
* ns32k-tdep.c (ns32k_register_name_32082): Update.
(ns32k_register_name_32382): Update.
* d10v-tdep.c (d10v_ts2_register_name): Update.
(d10v_ts3_register_name): Update.
* xstormy16-tdep.c (xstormy16_register_name): Update.
* vax-tdep.c (vax_register_name): Update.
* v850-tdep.c (v850_register_name): Update.
* m68hc11-tdep.c (m68hc11_register_name): Update.
* mn10300-tdep.c (mn10300_generic_register_name): Update.
(am33_register_name): Update.