fix link issues on aarch64 musl

The linker was unable to find __addtf3, __multf3 and __subtf3.

Added target-feature=+crt-static and link-arg=-lgcc as a temporary
workaround. This seems to be the accepted fix in the Rust community.

Signed-off-by: Andreea Florescu <fandree@amazon.com>

.cargo/config

@@ -0,0 +1,5 @@
+# This workaround is needed because the linker is unable to find __addtf3,
+# __multf3 and __subtf3.
+# Related issue: https://github.com/rust-lang/compiler-builtins/issues/201
+[target.aarch64-unknown-linux-musl]
+rustflags = [ "-C", "target-feature=+crt-static", "-C", "link-arg=-lgcc"]