refactor(codegen): emit and link bitcode files instead of object files

[baszalmstra]

Instead of emitting object files the compiler emits LLVM bitcode files. This enables LLD to understand the whole program which enables future further optimizations like LTO.

[codecov]

Codecov Report

Merging #258 into master will decrease coverage by 0.14%.
The diff coverage is 82.88%.

@@            Coverage Diff             @@
##           master     #258      +/-   ##
==========================================
- Coverage   78.63%   78.49%   -0.15%     
==========================================
  Files         212      215       +3     
  Lines       12681    12705      +24     
==========================================
+ Hits         9972     9973       +1     
- Misses       2709     2732      +23     

Impacted Files	Coverage Δ
crates/mun_codegen/src/code_gen.rs	100.00% <ø> (+12.50%)	⬆️
crates/mun_codegen/src/ir/types/test.rs	0.00% <0.00%> (ø)
crates/mun_codegen/src/linker.rs	22.35% <ø> (ø)
crates/mun_codegen/src/value/float_value.rs	0.00% <0.00%> (ø)
crates/mun_codegen_macros/src/lib.rs	0.00% <0.00%> (ø)
crates/mun_compiler/src/driver.rs	59.64% <ø> (ø)
crates/mun_runtime/tests/runtime.rs	100.00% <ø> (ø)
crates/mun_target/src/spec.rs	80.00% <ø> (ø)
crates/mun_target/src/spec/windows_msvc_base.rs	100.00% <ø> (ø)
crates/mun_codegen/src/value/string.rs	21.42% <25.00%> (ø)
... and 33 more

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