Improve zero-scratch-regs-*.c scan-asm regexps
and add target selectors for 32bit targets.

2020-11-03  Uroš Bizjak  <ubizjak@gmail.com>

gcc/testsuite/ChangeLog:

    * gcc.target/i386/zero-scratch-regs-1.c: Add ia32 target
    selector where appropriate.  Improve scan-assembler regexp.
    * gcc.target/i386/zero-scratch-regs-2.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-3.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-4.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-5.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-6.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-7.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-8.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-9.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-10.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-13.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-14.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-15.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-16.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-17.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-18.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-19.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-20.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-21.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-22.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-23.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-24.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-25.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-26.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-27.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-28.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-29.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-30.c: Ditto.
    * gcc.target/i386/zero-scratch-regs-31.c: Ditto.

Tested on x86_64-linux-gnu {,-m32} and pushed.

Uros.