So this fix doesn't work for me, if I pull the accuweather app from https://github.com/telefonicaid/firefoxos-gaia-latam/tree/master/external-apps/accuweather
I still get an exception.

Here is the best I could hack. It highlights the limits of doing such trick in Makefile.
Do you have a plan to eventually migrate this particular code to JS?
I mean the code that actually checks if we should rebuild the app or not.
Given that this code looks hacky, and prevent from correctly rebuilding incrementaly apps with `:` in filename,
it may be easier to first land a patch that always rebuild the app no matter what.
The special case of `:` isn't really important, but we may miss some other forbiden characters that are more common...

```
diff --git a/Makefile b/Makefile
index 2fa3d3f..8605ba4 100644
--- a/Makefile
+++ b/Makefile
@@ -474,16 +474,7 @@ include build/common.mk
 # if the app doesn't have any change.
 define app-makefile-template
 
-# FIXME: [bug 989918] this workaround is use to avoid crash if a file include
-# colon in its filename.
-ifneq (,$(shell find $(2) -name "*:*"))
-$(eval $(notdir $(2))_APP_FILES =)
-.PHONY: $(1)
-else
-$(eval $(notdir $(2))_APP_FILES = $(call rwildcard,$(2),*))
-endif
-
-$(1): $($(notdir $(2))_APP_FILES) $(XULRUNNER_BASE_DIRECTORY) | $(STAGE_DIR)
+$(1): $3 $(XULRUNNER_BASE_DIRECTORY) | $(STAGE_DIR)
        @if [[ ("$(2)" =~ "${BUILD_APP_NAME}") || (${BUILD_APP_NAME} == "*") ]]; then \
                if [ -r "$(2)/Makefile" ]; then \
                        echo "execute Makefile for $(notdir $(2)) app" ; \
@@ -517,8 +508,9 @@ test-agent-bootstrap: $(XULRUNNER_BASE_DIRECTORY)
 $(STAGE_DIR):
        mkdir -p $@
 
-$(foreach appdir,$(GAIA_APPDIRS), \
-       $(eval $(call app-makefile-template,$(STAGE_DIR)$(SEP)$(notdir $(appdir)),$(appdir))) \
+$(foreach appdir, $(GAIA_APPDIRS), \
+       $(eval deps=$(shell find $(appdir) -name "*:*" -prune -o -type f -print));\
+       $(eval $(call app-makefile-template,$(STAGE_DIR)$(SEP)$(notdir $(appdir)), $(appdir), $(deps)))\
 )
 
 # Keyboard app needs keyboard_layouts.json from |keyboard-layouts|
```