Add missing .PHONY in portable Makefile
The recipe "build-portable" is also the name of the generated directory.
Add this name to the .PHONY list.
# This is a simple Makefile because Meson is not flexible enough to execute some
# arbitrary commands.
-.PHONY: default clean release-portable dist-portable dist-portable-zip sums test check
+.PHONY: default clean build-portable release-portable dist-portable dist-portable-zip sums test check
GRADLE ?= ./gradlew
