Add support for limited pretty-printing of ARM PLT entries on eabi and nacl targets.

Add support for limited pretty-printing of ARM PLT entries on eabi and nacl targets.

    	* elf32-arm.c (elf32_arm_get_synthetic_symtab): Add new callback.
    	(elf32_arm_nacl_plt_sym_val): Likewise.
    	(elf32_arm_plt0_size): Add helper function.
    	(elf32_arm_plt_size): Likewise.

    	* ld-arm/arm-app-abs32.d: Updated test.
    	* ld-arm/arm-app.d: Likewise.
    	* ld-arm/arm-lib-plt32.d: Likewise.
    	* ld-arm/arm-lib.d: Likewise.
    	* ld-arm/armthumb-lib.d: Likewise.
    	* ld-arm/cortex-a8-fix-b-plt.d: Likewise.
    	* ld-arm/cortex-a8-fix-bcc-plt.d: Likewise.
    	* ld-arm/cortex-a8-fix-bl-plt.d: Likewise.
    	* ld-arm/cortex-a8-fix-bl-rel-plt.d: Likewise.
    	* ld-arm/cortex-a8-fix-blx-plt.d: Likewise.
    	* ld-arm/farcall-mixed-app-v5.d: Likewise.
    	* ld-arm/farcall-mixed-app.d: Likewise.
    	* ld-arm/farcall-mixed-lib-v4t.d: Likewise.
    	* ld-arm/farcall-mixed-lib.d: Likewise.
    	* ld-arm/ifunc-10.dd: Likewise.
    	* ld-arm/ifunc-14.dd: Likewise.
    	* ld-arm/ifunc-15.dd: Likewise.
    	* ld-arm/ifunc-3.dd: Likewise.
    	* ld-arm/ifunc-4.dd: Likewise.
    	* ld-arm/ifunc-7.dd: Likewise.
    	* ld-arm/ifunc-8.dd: Likewise.
    	* ld-arm/ifunc-9.dd: Likewise.
    	* ld-arm/long-plt-format.d: Likewise.
    	* ld-arm/mixed-app-v5.d: Likewise.
    	* ld-arm/mixed-app.d: Likewise.
    	* ld-arm/mixed-lib.d: Likewise.
    	* ld-arm/thumb2-bl-undefweak.d: Likewise.
    	* ld-arm/thumb2-bl-undefweak1.d: Likewise.