linker: `no such file` linking error on AArch64
When using default cc linker, we will have segfault.
Debugging with `rust-gdb`, the specific error is as follows:
src/string/memcpy.c: No such file or directory.
Only changing linker with `aarch64-linux-musl-gcc`, the
`rust-agent` could be totally statically linked and run successfully.
Fixes:
##
[target.aarch64-unknown-linux-musl]
+## Only setting linker with `aarch64-linux-musl-gcc`, the
+## `rust-agent` could be totally statically linked.
+linker = "aarch64-linux-musl-gcc"
+
## The __addtf3, __subtf3 and __multf3 symbols are used by aarch64-musl,
## but are not provided by rust compiler-builtins.
## For now, the only functional workaround accepted by rust communities
