Use custom libc implementation for RTEMS build

This should not be necessary anymore once, the changes are in upstream
libc

Author: thesummer

Cargo.toml

@@ -106,6 +106,7 @@ debug = 0
 strip = true
 
 [patch.crates-io]
+libc = { git = "https://github.com/thesummer/libc", rev = "2ada946801aec517051bb00cb83e890f9af5ad37" }
 # See comments in `library/rustc-std-workspace-core/README.md` for what's going on
 # here
 rustc-std-workspace-core = { path = 'library/rustc-std-workspace-core' }