RISC-V: PR28789, Reject R_RISCV_PCREL relocations with ABS symbol in PIC/PIE.

RISC-V: PR28789, Reject R_RISCV_PCREL relocations with ABS symbol in PIC/PIE.

The non-preemptible SHN_ABS symbol with a pc-relative relocation should be
disallowed when generating shared object (pic and pie).  Generally, the
following cases, which refer to pr25749, will cause a symbol be
non-preemptible,

* -pie, or -shared with -symbolic
* STV_HIDDEN, STV_INTERNAL, STV_PROTECTED
* Have dynamic symbol table, but without the symbol
* VER_NDX_LOCAL

However, PCREL_HI20/LO12 relocs are always bind locally when generating
shared object, so not only the non-preemptible absolute symbol need to
be disallowed, all absolute symbol references need but except that they
are defined in linker script.  If we also disallow the absolute symbol
in linker script, then the glibc-linux toolchain build failed, so regard
them as pc-relative symbols, just like what x86 did.

Maybe we should add this check for all pc-relative relocations, rather
than just handle in R_RISCV_PCREL relocs.  Ideally, since the value of
SHN_ABS symbol is a constant, only S - A relocations should be allowed
in the shared object, so only BFD_RELOC_8/16/32/64 are allowed, which
means R_RISCV_32/R_RISCV_64.

bfd/
    PR 28789
    * elfnn-riscv.c (riscv_elf_check_relocs): The absolute symbol cannot be
    referneced with pc-relative relocation when generating shared object.
ld/
    PR 28789
    * ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp: Updated.
    * ld/testsuite/ld-riscv-elf/pcrel-reloc*: New testcases.