testegl.c not building on rpi

Submitted by Guillaume Desmottes @gdesmott

Link to original bug (#796205)

Description

Trying to build gst-omx on the rpi:

testegl.c:68:22: fatal error: bcm_host.h: No such file or directory

This file is provided in /opt/vc/include/bcm_host.h

I tried passing -I/opt/vc/include/ so it can find it but then I'm hitting multi declarations in their EGL headers:

In file included from /opt/vc/include/interface/vcos/vcos.h:118:0,
from /opt/vc/include/interface/vmcs_host/vc_dispmanx.h:33,
from /opt/vc/include/EGL/eglplatform.h:110,
from /opt/vc/include/EGL/egl.h:36,
from testegl.c:42:
/opt/vc/include/interface/vcos/pthreads/vcos_platform.h:792:23: error: redundant redeclaration of ‘_vcos_thread_sem_wait’ [-Werror=redundant-decls]
VCOS_INLINE_DECL void _vcos_thread_sem_wait(void);
^~~~~~~~~~~~~~~~~~~~~
/opt/vc/include/interface/vcos/pthreads/vcos_platform.h:644:6: note: previous definition of ‘_vcos_thread_sem_wait’ was here
void _vcos_thread_sem_wait(void) {

I'm not familiar with the rpi headers so I'm not sure of what's the proper fix here.