[ELF][RISCV] Allow PT_LOAD to have overlapping p_offset ranges on EM_RISCV

[ELF][RISCV] Allow PT_LOAD to have overlapping p_offset ranges on EM_RISCV

Port the D64906 technique to RISC-V. It deletes 3 alignments at
PT_LOAD boundaries for the default case: the size of a RISC-V binary
decreases by at most 12kb.

llvm-svn: 370192