Resolve libm relative to sysroot

[trnila]

aarch64-none-linux-gnu needs to search for libm within its sysroot, otherwise error occurs with -lm:

external/+arm_toolchain+aarch64_none_linux_gnu_linux_x86_64/bin/../lib/gcc/aarch64-none-linux-gnu/13.2.1/../../../../aarch64-none-linux-gnu/bin/ld: cannot find /lib64/libm.so.6: No such file or directory
external/+arm_toolchain+aarch64_none_linux_gnu_linux_x86_64/bin/../lib/gcc/aarch64-none-linux-gnu/13.2.1/../../../../aarch64-none-linux-gnu/bin/ld: cannot find /lib64/libmvec.so.1: No such file or directory

[hexdae]

Thanks!