build: add option to exclude executables/dirs from being stripped

Sometimes it may be desirable to keep debug symbols for some binaries and
libraries on the target. This commit introduces the config option
BR2_STRIP_EXCLUDE_FILES, which is interpreted as a list of such binaries
and libraries, and the option BR2_STRIP_EXCLUDE_DIRS, which indicates
directories excluded from stripping entirely.
These exclusions are passed to the find command in the target-finalize step.

Signed-off-by: Sven Neumann <s.neumann@raumfeld.com>
Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
diff --git a/Makefile b/Makefile
index 9a9634d..c691767 100644
--- a/Makefile
+++ b/Makefile
@@ -386,6 +386,13 @@
 
 $(TARGET_DIR): $(BUILD_DIR)/.root
 
+STRIP_FIND_CMD = find $(TARGET_DIR)
+ifneq (,$(call qstrip,$(BR2_STRIP_EXCLUDE_DIRS)))
+STRIP_FIND_CMD += \( $(call finddirclauses,$(TARGET_DIR),$(call qstrip,$(BR2_STRIP_EXCLUDE_DIRS))) \) -prune -o
+endif
+STRIP_FIND_CMD += -type f -perm +111
+STRIP_FIND_CMD += -not \( $(call findfileclauses,libthread_db*.so* $(call qstrip,$(BR2_STRIP_EXCLUDE_FILES))) \) -print
+
 target-finalize:
 ifeq ($(BR2_HAVE_DEVFILES),y)
 	( support/scripts/copy.sh $(STAGING_DIR) $(TARGET_DIR) )
@@ -410,8 +417,7 @@
 ifeq ($(BR2_PACKAGE_PYTHON_PYC_ONLY),y)
 	find $(TARGET_DIR)/usr/lib/ -name '*.py' -print0 | xargs -0 rm -f
 endif
-	find $(TARGET_DIR) -type f -perm +111 '!' -name 'libthread_db*.so*' | \
-		xargs $(STRIPCMD) 2>/dev/null || true
+	$(STRIP_FIND_CMD) | xargs $(STRIPCMD) 2>/dev/null || true
 	find $(TARGET_DIR)/lib/modules -type f -name '*.ko' | \
 		xargs -r $(KSTRIPCMD) || true