[ng] perf: disable GNU make builtin rules, for performance reasons

* lib/am/header-vars (MAKEFLAGS): Append '--no-builtin-rules'.  This
enhance performance by removing GNU make builtin rules that would be
rather irrelevant (e.g., rules to automatically check out files from
from RCS or SCCS repositories), or overridden by Automake (e.g., rules
to compile C or C++ files).  With this simple tweak, the null-build
time on GNU coreutils on an aging Debian system goes down from ~ 20
seconds to ~ 9 seconds.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>

diff --git a/lib/am/header-vars.am b/lib/am/header-vars.am
index eccfec58c9078fc4c4d182f325dde691e09eeff3..75e5a3a8885ce8b4d5321cf02a692227dd520ae8 100644 (file)
--- a/lib/am/header-vars.am
+++ b/lib/am/header-vars.am
@@ -16,6 +16,13 @@
 
 VPATH = @srcdir@
 
+## Enhance performance by removing GNU make builtin rules that would be
+## rather irrelevant (e.g., rules to automatically check out files from
+## from RCS or SCCS repositories), or overridden by Automake (e.g., rules
+## to compile C or C++ files).  For larger packages (like GNU coreutils),
+## this can greatly speed up null or almost-null builds, up to even 50%!
+MAKEFLAGS += --no-builtin-rules
+
 ## Declare an error, without immediately terminating the execution (proper
 ## code will take care later of that).  This will allow us to diagnose more
 ## issues at once, rather than stopping at the first one.