Log message:
lang/qbe: Update to 1.2

QBE 1.2 comes with important correctness fixes as well as improvements to the
documentation. Notable changes are:

- correctness fixes to the stack-slot coalescing pass
- new experimental dbgfile and dbgloc directives

Log message:
lang/qbe: Update to 1.1

Changes from 1.0:

- support for Apple ARM-based hardware (arm64_apple target)
- support for thread-local storage
- a new blit instruction to copy small aggregates
- a new hlt instruction to flag non-termination
- a new stack slot coalescing optimization

Log message:
lang/qbe: Import package

QBE aims to be a pure C embeddable backend that provides 70% of the
performance of advanced compilers in 10% of the code. Its small size serves
both its aspirations of correctness and our ability to understand, fix, and
improve it. It also serves its users by providing trivial integration and
great flexibility.