README,manibuilder: Update environment overrides for DJGPP

The currently documented DJGPP setup doesn't utilize pkg-config, hence
we have to specify the presence of libpci explicitly.

Change-Id: I1e5cc9e0235fd49948edd9d39087735b8685638e
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/73776
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
2 files changed