'make clean' loops cleaning nss #556
Description
I tried to build servo in-tree and ran into #378. When I try to clean up with make clean it goes into an infinite loop:
...
make[197]: Entering directory `/home/keegan/proj/servo/servo/src/support/nss/nss'
make -j1 -C /home/keegan/proj/servo/servo/src/support/nss/nss clean
make[198]: Entering directory `/home/keegan/proj/servo/servo/src/support/nss/nss'
make -j1 -C /home/keegan/proj/servo/servo/src/support/nss/nss clean
...
Servo is on master = fdb0d82