freerdp: fix build with uclibc snapshot and uclibc-ng

uclibc snapshot and uclibc-ng add support for the eventfd_{read,write} glibc
extensions. Refine our uClibc support patch to take this into account, based
on upstream fix applied to freerdp master branch.

Fixes:
http://autobuild.buildroot.net/results/e6c/e6c2ac69682f409f9ee78a3a6155ae356c3368a4/
http://autobuild.buildroot.net/results/558/558ccb0e475bfb434685c580d86f6c634238a084/
http://autobuild.buildroot.net/results/249/24901b2dfc92b516f74054ea7bb71e1ccfc3f12f/



and many more.

Cc: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>