support/dependencies: check for system-provided bison and flex

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

support/dependencies/check-host-bison-flex.mk

@@ -0,0 +1,10 @@
+# If the system lacks bison or flex, add
+# dependencies to suitable host packages
+
+ifeq ($(shell which bison 2>/dev/null),)
+BR2_BISON_HOST_DEPENDENCY = host-bison
+endif
+
+ifeq ($(shell which flex 2>/dev/null),)
+BR2_FLEX_HOST_DEPENDENCY = host-flex
+endif