jenkinsfile: try to fix target mapping lookup

Jenkinsfile

@@ -1,4 +1,5 @@
-def targetMapping = [
+def getGCCTarget(rust_target) {
+	targetMapping = [
     	"mips-unknown-linux-musl": "mips-linux-muslsf",
     	"mips64-unknown-linux-muslabi64": "mips64-linux-musl",
     	"mips64el-unknown-linux-muslabi64": "mips64el-linux-musl",
@@ -6,7 +7,6 @@ def targetMapping = [
     	"x86_64-unknown-linux-musl": "x86_64-linux-musl"
     ]
 
-def getGCCTarget(rust_target) {
 	return targetMapping[rust_target]
 }