servo: Merge #1292 - Disable parallel builds at top level (from metajack:not-parallel); r=larsbergstrom

Sub-builds are still parallelized. This is a workaround for rustpkg
issues. See rust-lang/rust#9650

Source-Repo: https://github.com/servo/servo
Source-Revision: eb9b82fed8717dc9970489e2856ac95b73a6e9eb

UltraBlame original commit: d89c91a96214d2327057e37bef504ac7c4f7501d

Author: marco-c

servo/Makefile.in

@@ -378,3 +378,6 @@ backup-rust:
 
 restore-rust:
 	if [ -d ../$(CFG_TARGET_TRIPLES) ]; then rm -rf $(B)src/compiler/rust; mv ../$(CFG_TARGET_TRIPLES) $(B)src/compiler/rust; fi
+
+.NOTPARALLEL:
+