Replace build script with a smart wrapper

If a user simply types `make` it will run in parallel by default, which
is what we want to do in most cases.

CMakeLists.txt

@@ -295,3 +295,9 @@ add_custom_target (distclean
 	COMMENT Removing CMake-generated files
 	VERBATIM
 	)
+
+# smart wrapper that auto-parallelizes builds
+file (COPY
+	GNUmakefile
+	DESTINATION ${PROJECT_BINARY_DIR}
+	)

GNUmakefile

@@ -0,0 +1,30 @@
+# GNUmakefile is processed before Makefile, which is why we arrive here
+# first; when we call the other makefile, then we must specify its real
+# name with the -f parameter
+
+# figure out the number of processors from the system, add one and round
+# to nearest integer. this is the maximum number of processes we want running
+# at the same time (one for each core and one stuck on I/O)
+PROCS:=$(shell echo "("$$(grep -P -c '^processor\t:' /proc/cpuinfo)+1")"/1 | bc)
+
+# use these utilities if they are available
+IONICE:=$(shell test -x "$$(which ionice)" && echo ionice -c2 -n7)
+NICE:=$(shell test -x "$$(which nice)" && echo nice)
+
+# ignore that there may be files with these names, we are going to call
+# the other make regardless
+.PHONY: __everything $(MAKECMDGOALS)
+
+# outsource the processing to the real makefile, running in parallel and
+# in a nice environment so that it doesn't hog our workstation. if there
+# is nothing else happening on the box, then it will run just as fast
+__everything:
+	@$(IONICE) $(NICE) $(MAKE) -f Makefile -j $(PROCS) $(MAKECMDGOALS)
+
+# automatically generate all the goals we are asked to make and delegate
+# processing of them to the real makefile through the dependency (since
+# everything depends on the same thing, then we only call the other make
+# once). the dummy command is just there to make sure that make doesn't
+# show the "Nothing to do for `foo'" message after processing
+$(MAKECMDGOALS): __everything
+	@true

build

@@ -1,2 +0,0 @@
-#!/bin/sh
-exec ionice -c2 -n7 nice make -j $(echo "("$(grep -P -c '^processor\t:' /proc/cpuinfo)+1")"/1 | bc) "$@"