error for non-system, non-vendor fuzzer

We should fix the system/vendor cases before
opening this up to more variants.

Fixes: 317926582
Test: build
Change-Id: I7e06059249b6df055c08bc9a78c2e07f2016fe52
diff --git a/cc/fuzz.go b/cc/fuzz.go
index 0aa9d4b..2b91c57 100644
--- a/cc/fuzz.go
+++ b/cc/fuzz.go
@@ -182,9 +182,13 @@
 }
 
 func (fuzz *fuzzBinary) linkerFlags(ctx ModuleContext, flags Flags) Flags {
-	subdir := "lib"
-	if ctx.inVendor() {
+	var subdir string
+	if ctx.isForPlatform() {
+		subdir = "lib"
+	} else if ctx.inVendor() {
 		subdir = "lib/vendor"
+	} else {
+		ctx.ModuleErrorf("Fuzzer must be system or vendor variant")
 	}
 
 	flags = fuzz.binaryDecorator.linkerFlags(ctx, flags)