Use `fastcc` calling convention

[mbg]

This changes the code generator to use the fastcc calling convention where possible and sets appropriate linkage types:

• The fastcc calling convention supports tail-call elimination and facilitates the first step towards some performance improvements.
• This required the addition of some utility functions on top of those provided by llvm-hs-pure to customise the calls and functions emitted.
• Setting more specific linkage types allows the LLVM optimiser to perform better dead code elimination. For example, in the cast of the factorial program, the LLVM IR can be reduced to around 1k lines through dead code elimination.

[github-actions[bot]]

Test results (ubuntu-latest)

0 files   -     1  0 suites   - 1   0s :stopwatch: -39s 0 tests  - 136  0 :heavy_check_mark:  - 136  0 :zzz: ±0  0 :x: ±0 

Results for commit b3966894. ± Comparison against base commit e13eae1d.

This pull request removes 136 tests.

``` test/Spec.hs.data ‑ Data constants: bytestring test/Spec.hs.data ‑ Data constants: constructors test/Spec.hs.data ‑ Data constants: integer test/Spec.hs.data ‑ Data constants: list test/Spec.hs.data ‑ Data constants: map test/Spec.hs.data ‑ bData test/Spec.hs.data ‑ chooseData: bytestring test/Spec.hs.data ‑ chooseData: constructors test/Spec.hs.data ‑ chooseData: integer test/Spec.hs.data ‑ chooseData: list … ```

[github-actions[bot]]

Test results (macos-latest)

0 files   -     1  0 suites   - 1   0s :stopwatch: - 1m 43s 0 tests  - 136  0 :heavy_check_mark:  - 136  0 :zzz: ±0  0 :x: ±0 

Results for commit b3966894. ± Comparison against base commit e13eae1d.

This pull request removes 136 tests.

``` test/Spec.hs.data ‑ Data constants: bytestring test/Spec.hs.data ‑ Data constants: constructors test/Spec.hs.data ‑ Data constants: integer test/Spec.hs.data ‑ Data constants: list test/Spec.hs.data ‑ Data constants: map test/Spec.hs.data ‑ bData test/Spec.hs.data ‑ chooseData: bytestring test/Spec.hs.data ‑ chooseData: constructors test/Spec.hs.data ‑ chooseData: integer test/Spec.hs.data ‑ chooseData: list … ```