tools/Config.mk: Move the RWILDCARD function definition from apps/builtin/Makefile to nuttx/tools/Config.mk. It may have a broader usage than it does now.

tools/Config.mk

@@ -269,6 +269,7 @@ endef
 endif
 
 # CATFILE - Cat and append a list of files
+#
 # USAGE: $(call CATFILE,dest,src1,src2,src3,...)
 
 ifeq ($(CONFIG_WINDOWS_NATIVE),y)
@@ -281,6 +282,19 @@ define CATFILE
 endef
 endif
 
+# RWILDCARD - Recursive wildcard used to get lists of files from directories
+#
+# USAGE:  FILELIST = $(call RWILDCARD,<dir>,<wildcard-filename)
+#
+# This is functionally equivent to the fillowing, but has the advantage in
+# that it is portable
+#
+# FILELIST = ${shell find <dir> -name <wildcard-file>}
+
+define RWILDCARD
+  $(foreach d,$(wildcard $1/*),$(call RWILDCARD,$d/)$(filter $(subst *,%,$2),$d))
+endef
+
 # CLEAN - Default clean target
 
 ifeq ($(CONFIG_WINDOWS_NATIVE),y)