[ELF] Change (NOLOAD) type mismatch to use SHT_NOBITS instead of SHT_PROGBITS

Placing a non-SHT_NOBITS input section in an output section specified with
(NOLOAD) is fishy but used by some projects. D118840 changed the output type to
SHT_PROGBITS, but using the specified type seems to make more sense and improve
GNU ld compatibility: `(NOLOAD)` seems to change the output section type
regardless of input.

I think we should keep the current type mismatch warning as it does indicate an
error-prone usage.

Reviewed By: peter.smith

Differential Revision: https://reviews.llvm.org/D125074