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).

2 files changed, 2 insertions, 2 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
diff --git a/changelog b/changelog
index 53683a2..0ecf65c 100644
--- a/changelog
+++ b/changelog
@@ -29,7 +29,7 @@ gcc-8 (8.3.0+sip1-1) trunk
   * Replace "/gcc-<version>/" and "/c++-<version>/" with "/gcc/<version>/" and
     "/c++/<version>/" respectively in directory paths.
   * Use automatic shared library dependencies.
-  * Build with 4 parallel jobs by default.
+  * By default, build with as many parallel jobs as there are online CPUs.
 
  -- Patrick McDermott <patrick.mcdermott@libiquity.com>  Thu, 02 May 2019 16:20:43 -0400