libosmocore libusb integration

Osmocom applications typically use libosmocore select.[ch] event loop
code as their main event dispatch mechanism.  When they want to deal
with libusb in a non-blocking/asynchronous way, they need to integrate
libusb into that select().

The new libosmousb is doing exactly that: Providing a shared utility
library for Osmocom programs that wish to use libusb.  This is useful
for example in simtrace2 host utilitie as well as osmo-e1d.

Change-Id: I656a1a38cbb5b1f3a9145d2869d3b4d0adefcae3
Closes: OS#4299
diff --git a/contrib/jenkins_arm.sh b/contrib/jenkins_arm.sh
index 8ee90f0..c9cd922 100755
--- a/contrib/jenkins_arm.sh
+++ b/contrib/jenkins_arm.sh
@@ -19,6 +19,7 @@
 	--disable-doxygen \
 	--disable-shared \
 	--disable-libsctp \
+	--disable-libusb \
 	--enable-external-tests \
 	CFLAGS="-Os -ffunction-sections -fdata-sections -nostartfiles -nodefaultlibs $WERROR_FLAGS"