Fixes the following build failures:

pth_mctx.c: In function '__pth_mctx_set':
pth_mctx.c:480:2: error: #error "Unsupported Linux (g)libc version
and/or platform"
 #error "Unsupported Linux (g)libc version and/or platform"
  ^
Makefile:991: recipe for target 'pth_mctx.lo' failed

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>