Alignment of symbol is not kept during linking

[Yuxuan Shui via Digitalmars-d]

I'm trying to build LDC with dmd and Musl, but the result ldc 
will always crash. I track that down to an unalignment SIMD 
access to a global variable. Apparently C++ compiler thinks the 
variable should be aligned to 16 bytes, but it's only aligned to 
8 bytes.

After some more digging, I find out dmd does try to do the right 
thing here. In the .o file, the offending symbol is indeed 
aligned to 16 bytes. But, after linking, that symbol got bumped 8 
bytes for some reason.

I searched around, and there seems to be no way to specify 
alignment on symbol, so I don't think the linker is in the wrong 
here.

C compilers would not put variables like that in .data, instead 
they use SHN_COMMON, and specify alignment there. LDC will just 
put every symbol into their own section, which also supports 
alignment. dmd should probably do the same.