xlat: avoid fork bombing the build system
xlat: avoid fork bombing the build system

When there were fewer xlat headers, this didn't matter as much.
But now with >200, trying to run them all in parallel can easily
fork bomb smaller systems.

* xlat/gen.sh (main): Do not more jobs than # of cpus.

TeamExodus/external_strace,Yu-AndroidM/android_external_strace,TeamExodus/external_strace,cuviper/strace,Saruta/strace,geekboxzone/mmallow_external_strace,geofft/strace,kapdop/android_external_strace,Distrotech/strace,Infinitive-OS/platform_external_strace,YUPlayGodDev/platform_external_strace,bigzz/strace_android,AOSP-YU/platform_external_strace,geofft/strace,kapdop/android_external_strace,Infinitive-OS/platform_external_strace,vrastogi/strace,bigzz/strace_android,kapdop/android_external_strace,Infinitive-OS/platform_external_strace,Infinitive-OS/platform_external_strace,MonkeyZZZZ/platform_external_strace,cuviper/strace,geekboxzone/mmallow_external_strace,Yu-AndroidM/android_external_strace,MonkeyZZZZ/platform_external_strace,Infinitive-OS/platform_external_strace,MonkeyZZZZ/platform_external_strace,Saruta/strace,kapdop/android_external_strace,geekboxzone/mmallow_external_strace,Distrotech/strace,vrastogi/strace,geekboxzone/mmallow_external_strace,YUPlayGodDev/platform_external_strace,Yu-AndroidM/android_external_strace,MonkeyZZZZ/platform_external_strace,Saruta/strace,Distrotech/strace,Yu-AndroidM/android_external_strace,bigzz/strace_android,geofft/strace,bigzz/strace_android,YUPlayGodDev/platform_external_strace,cuviper/strace,TeamExodus/external_strace,Yu-AndroidM/android_external_strace,Saruta/strace,AOSP-YU/platform_external_strace,AOSP-YU/platform_external_strace,cuviper/strace,geofft/strace,Distrotech/strace,kapdop/android_external_strace,MonkeyZZZZ/platform_external_strace,TeamExodus/external_strace,bigzz/strace_android,geofft/strace,cuviper/strace,Saruta/strace,geekboxzone/mmallow_external_strace,vrastogi/strace,vrastogi/strace,TeamExodus/external_strace,Distrotech/strace,YUPlayGodDev/platform_external_strace,vrastogi/strace,AOSP-YU/platform_external_strace,YUPlayGodDev/platform_external_strace,AOSP-YU/platform_external_strace