toolchain: modify the wildcard logic for shared libraries copying

Until now, the copy_toolchain_lib_root function took as argument the
base name of a library (e.g: libm.so), and was assuming that the usual
scheme libm.so.<x> being a symbolic link to the real library was used.

However, with musl based toolchains, the C library is named libc.so
directly, with no symbolic link at all. Therefore, this commit changes
the copy_toolchain_lib_root to move the responsibility of using a
wildcard or not after the library name the caller's responsibility.

So, all the existing LIB_EXTERNAL_LIBS values are modified to have a
.* at the end, so that the behavior is effectively unchanged.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>