Bug 1586100 - Only depend on js/src/export when it is available. r=dm…

…ajor

Differential Revision: https://phabricator.services.mozilla.com/D51978

config/recurse.mk

@@ -190,7 +190,11 @@ build/clang-plugin/tests/target-objects: build/clang-plugin/host
 # clang-plugin tests require js-confdefs.h on js standalone builds and mozilla-config.h on
 # other builds, because they are -include'd.
 ifdef JS_STANDALONE
+# The js/src/export target only exists when CURRENT_TIER is export. If we're in a later tier,
+# we can assume js/src/export has happened anyways.
+ifeq ($(CURRENT_TIER),export)
 build/clang-plugin/tests/target-objects: js/src/export
+endif
 else
 build/clang-plugin/tests/target-objects: mozilla-config.h
 endif