Add SSA optimizer and target

[SamuraiCrow]

Static Single-Assign format reduces complexity in modern compilers. It is used extensively in LLVM but is more practically applied in the use of the QBE backend. Since QBE is MIT licensed and much smaller than LLVM or even GCC, it would seem to be the most obvious target. What is needed to make QBE usable for E is:

• Add 32-bit processor support to the format using an existing patch
• Replace C11 dependencies with E equivalents (eg. fprintf with VfPrintF from DOS.library and printf with PrintF)

Compromises:

• Inline assembly is not supported by this optimizer target
• Register loading is automatic rather than REG variables and assumed because it has a proper register mapper and spiller.

[SamuraiCrow]

Depends on #9

[SamuraiCrow]

The 32-bit proposed patch is at https://lists.sr.ht/~mpu/qbe/patches/56712

[SamuraiCrow]

https://github.com/AmigaSchool/libqbe may be able to filter out some of the noise on the normal QBE build. It separates the parser for the QBE language from the actual code generator.