devel/openocd: Fix build with -fno-common
Fix the build of devel/openocd with -fno-common. The patch is based on the
upstream fix.
MFH: 2020Q3 (implicit, -fno-common fixes, ok by joenum)
Assume "pkg-config libusb*" works after 9.x EOL
FreeBSD appears to use different pkg-config name for 0.1.x API but it
doesn't matter much as 0.1, 1.0 and 2.0 share CFLAGS/LIBS.