RISC-V: Added ld testcases for the medlow and medany code models.

RISC-V: Added ld testcases for the medlow and medany code models.

There are two linker scripts, code-model-01.ld and code-model-02.ld,
which are corresponding to the two different memory layouts,

* code-model-01.ld: the text section is in the 32-bit address range, but
  the data section is far away from the text section, which means the data
  section is over the 32-bit address range.

* code-model-02.ld: the text section is over the 32-bit address range, but
  the data section is placed nearly zero address.

We use the two linker scripts, to test the current medlow and medany behaviors
of GNU ld, including the weak symbol references and the relaxations behaviors.
Besides, these testcases also show the limits of the current medlow and medany
code models, that is - we may get the truncated to fit errors when linking
with the above two linker scripts.

ld/
	* testsuite/ld-riscv-elf/code-model-01.ld: New testcases to test the
	behaviors of the current medlow and medany code models.
	* testsuite/ld-riscv-elf/code-model-02.ld: Likewise.
	* testsuite/ld-riscv-elf/code-model-medany-01.d: Likewise.
	* testsuite/ld-riscv-elf/code-model-medany-02.d: Likewise.
	* testsuite/ld-riscv-elf/code-model-medany-weakref-01.d: Likewise.
	* testsuite/ld-riscv-elf/code-model-medany-weakref-02.d: Likewise.
	* testsuite/ld-riscv-elf/code-model-medlow-01.d: Likewise.
	* testsuite/ld-riscv-elf/code-model-medlow-02.d: Likewise.
	* testsuite/ld-riscv-elf/code-model-medlow-weakref-01.d: Likewise.
	* testsuite/ld-riscv-elf/code-model-medlow-weakref-02.d: Likewise.
	* testsuite/ld-riscv-elf/code-model-relax-medany-01.d: Likewise.
	* testsuite/ld-riscv-elf/code-model-relax-medany-02.d: Likewise.
	* testsuite/ld-riscv-elf/code-model-relax-medany-weakref-01.d: Likewise.
	* testsuite/ld-riscv-elf/code-model-relax-medany-weakref-02.d: Likewise.
	* testsuite/ld-riscv-elf/code-model-relax-medlow-01.d: Likewise.
	* testsuite/ld-riscv-elf/code-model-relax-medlow-02.d: Likewise.
	* testsuite/ld-riscv-elf/code-model-relax-medlow-weakref-01.d: Likewise.
	* testsuite/ld-riscv-elf/code-model-relax-medlow-weakref-02.d: Likewise.
	* testsuite/ld-riscv-elf/code-model.s: Likewise.
	* testsuite/ld-riscv-elf/ld-riscv-elf.exp: Updated.