package/musl: fix conflict with riscv kernel headers

Add two upstream patches fixing musl vs kernel headers conflict. This
fixes build of strace for risc64 at it happens to use headers from both
sources.

Modify patch #3 to leave a single newline in user.h. Otherwise 'patch
-E' in apply-patches.sh deletes user.h instead of leaving it empty.

Fixes (strace):
http://autobuild.buildroot.net/results/ac32e83dc5eb5ce2809fc4b9d11f540dbdae9ed6/



Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>