Add OpenMP dependency to pkgconfig file if needed

cmake/openblas.pc.in

@@ -7,5 +7,5 @@ Name: OpenBLAS
 Description: OpenBLAS is an optimized BLAS library based on GotoBLAS2 1.13 BSD version
 Version: @OPENBLAS_VERSION@
 URL: https://github.com/xianyi/OpenBLAS
-Libs: -L${libdir} -lopenblas${libsuffix}
+Libs: @OpenMP_C_FLAGS@ -L${libdir} -lopenblas${libsuffix} 
 Cflags: -I${includedir}