Full cgo support

[cpunion]

• Basic cgo support
  • [x] Call c functions by cgo
  • [x] Mix cgo and LLGoPackage/LLGoFiles
• Full cgo support
  • [x] Preamble code compiling and cgo flags/pkg-config process
  • [x] C files auto compiling in package directory
  • [x] Test coverage & refactor
• Future works (not here)
  • C ABI compatiblely (struct params larger than 2 ptr size not working, should pass by ref)

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 40.08811% with 136 lines in your changes missing coverage. Please review.

Project coverage is 95.45%. Comparing base (ea654ef) to head (6114313).

Files with missing lines	Patch %	Lines
cl/instr.go	0.00%	59 Missing :warning:
cl/compile.go	34.14%	45 Missing and 9 partials :warning:
ssa/expr.go	0.00%	18 Missing :warning:
cl/import.go	50.00%	3 Missing and 1 partial :warning:
internal/buildtags/buildtags.go	98.33%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #866 +/- ## ========================================== - Coverage 97.62% 95.45% -2.17% ========================================== Files 20 21 +1 Lines 5971 6188 +217 ========================================== + Hits 5829 5907 +78 - Misses 120 248 +128 - Partials 22 33 +11 ```

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