RISC-V: Don't generate R_RISCV_RELATIVE if symbol referenced section is SH_ABS

It's werid if it's absolute symbol but have a relative reloc for got entry
under pie.  So don't generate relative reloc if symbol referenced section is
SH_ABS.  However, x86 allows the absolute symbol defined in linker script has
a relative reloc, not sure if risc-v needs this or not.