build: Base jobs on number of CPUs

This is how BusyBox's `nproc --all` works.  It's Linux-specific, but the
alternatives are the (BusyBox) nproc utility (non-standard and currently
disabled in ProteanOS) and the getconf utility (standard but provided by
glibc and not in musl) with the _NPROCESSORS_ONLN operand (non-standard
but common in standard C libraries).

1 files changed, 1 insertions, 1 deletions

diff --git a/build b/build
index 299b291..ff2d7dd 100755
--- a/build
+++ b/build
@@ -96,7 +96,7 @@ dir_macros = \
 extra_opts =
 native_target = bootstrap-lean
 cross_target = all-gcc
-jobs = 4
+jobs = $$(printf '%s\n' /sys/devices/system/cpu/cpu[0-9]* | wc -l)
 include ../local.mk
 # For example, to disable bootstrapping, set these in local.mk:
 #     extra_opts = --disable-bootstrap