Otherwise, the availability of these variables depends on what
happened to be available at the time the PostgreSQL build was
configured.
top_srcdir = $(top_builddir)
srcdir = .
VPATH =
+
+# These might be set in Makefile.global, but if they were not found
+# during the build of PostgreSQL, supply default values so that users
+# of pgxs can use the variables.
+ifeq ($(BISON),)
+BISON = bison
+endif
+ifeq ($(FLEX),)
+FLEX = flex
+endif
endif