Remove -c flag. Erroneous output caused on android

While cross-building for android, the -c flag was causing errors.
This -c option ends up in Libs.private of libusb-1.0.pc file.
On its usage, it is interpreted as "Compile and assemble, but do not link"
option of gcc. Usage of -c in this way might be unintended.
Hence, removing this option.

Signed-off-by: Venkatesh Shukla <venkatesh.shukla.eee11@iitbhu.ac.in>