Unable to load lib_c on hosts with triple without libc

[GeopJr]

Bug Report

Some triples miss the libc part of the environment.
Examples:

• x86_64-suse-linux
• x86_64-redhat-linux
• more

This creates two issues:

1. CrystalPath#add_target_path can't load lib_c as x86_64-linux doesn't match any.
2. Codegen::Target#gnu? & Codegen::Target#musl? are both false.

Reproduction

1. Host is one of the above mentioned examples.
2. $ make all
3. $ make compiler_spec

In src/exception/call_stack/libunwind.cr:1:1

 1 | require "c/dlfcn"
     ^
Error: can't find file 'c/dlfcn'

If you're trying to require a shard:
- Did you remember to run `shards install`?
- Did you make sure you're running the compiler in the same directory as your shard.yml?
make: *** [Makefile:180: .build/compiler_spec] Error 1

Crystal

Using compiled compiler at .build/crystal
Crystal 1.6.1-dev [809c49e] (2022-10-11)

LLVM: 14.0.6
Default target: x86_64-suse-linux