Clarify unit of size in docs for size_of functions.
Changed the docs in mem.rs to clarify the fact the the size functions return sizes in bytes.
Regression test closes #7660
Fix staticlib outputs linking to blank archives

When creating a staticlib, it unzips all static archives it finds and then
inserts the files manually into the output file. This process is done through
`ar`, and `ar` doesn't like if you specify you want to add files and you don't
give it any files.

This case arose whenever you linked to an archive that didn't have any contents
or all of the contents were filtered out. This just involved ignoring the case
where the number of inputs we have is 0, because we don't have any files to add
anyway.
Fix bug with zero-length filemaps and rename bytepos_to_local_charpos to bytepos_to_charpos.
auto merge of #12374 : dylanbraithwaite/rust/size_of_unit_clarification, r=cmr

Changed the docs for std::mem to clarify the fact that the size functions return sizes in bytes.
auto merge of #12375 : FlaPer87/rust/issue-7660, r=cmr
auto merge of #12379 : alexcrichton/rust/fix-ar-thing, r=brson

When creating a staticlib, it unzips all static archives it finds and then
inserts the files manually into the output file. This process is done through
`ar`, and `ar` doesn't like if you specify you want to add files and you don't
give it any files.

This case arose whenever you linked to an archive that didn't have any contents
or all of the contents were filtered out. This just involved ignoring the case
where the number of inputs we have is 0, because we don't have any files to add
anyway.
auto merge of #11904 : nick29581/rust/0filemap, r=alexcrichton
Don't recurse twice into ExprParen in vtable checking.
Replaced method_map_entry with method_origin and cleaned up vtable checking a bit.
Resolve the vtables for method calls to generic Drop impls with trait bounds.