contrib/jenkins.sh: Fix missing nvic.h

if we don't call 'make' in libopencm3 of a clean install, we will be
missing some generated nvic.h header files and compilation will fail
like below:

In file included from ../../libopencm3//include/libopencm3/cm3/nvic.h:147,
                 from ../../librfn/librfn/libopencm3/console_stm32.c:24:
../../libopencm3//include/libopencm3/dispatch/nvic.h:8:11: fatal error: libopencm3/stm32/f1/nvic.h: No such file or directory
 # include <libopencm3/stm32/f1/nvic.h>
           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

contrib/jenkins.sh

@@ -11,6 +11,9 @@ publish="$1"
 git submodule init
 git submodule update
 
+# build the library once so that the irq2nvic script is running, generating headers
+(cd libopencm3 && make)
+
 echo "=============== libopencm3 START  =============="
 cd "$TOPDIR"
 make $PARALLEL_MAKE lib