Merge #52

52: Only checking for necessary extensions when linking, made debug information location-independent r=almindor a=ilya-epifanov

Regarding the debug information:
```diff
1c1
< In archive src/oss/riscv-rt-orig/bin/riscv32i-unknown-none-elf.a:
---
> In archive src/oss/riscv-rt/bin/riscv32i-unknown-none-elf.a:
335,336c335,336
<     <18>   DW_AT_comp_dir    : (indirect string, offset: 0x6): /home/disasm/dev/rust/embedded/workspace/riscv-rt
<     <1c>   DW_AT_producer    : (indirect string, offset: 0x38): GNU AS 2.32
---
>     <18>   DW_AT_comp_dir    : (indirect string, offset: 0x6): /riscv-rt
>     <1c>   DW_AT_producer    : (indirect string, offset: 0x10): GNU AS 2.34
367,371c367,368
<   0x00000000 61736d2e 53002f68 6f6d652f 64697361 asm.S./home/disa
<   0x00000010 736d2f64 65762f72 7573742f 656d6265 sm/dev/rust/embe
<   0x00000020 64646564 2f776f72 6b737061 63652f72 dded/workspace/r
<   0x00000030 69736376 2d727400 474e5520 41532032 iscv-rt.GNU AS 2
<   0x00000040 2e333200                            .32.
---
>   0x00000000 61736d2e 53002f72 69736376 2d727400 asm.S./riscv-rt.
>   0x00000010 474e5520 41532032 2e333400          GNU AS 2.34.
386c383
<   Version:               1
---
>   Version:               3
```

Versions are still different, but at least the build paths are independent from the build environment.

Co-authored-by: Ilya Epifanov <elijah.epifanov@gmail.com>