Makefile: delete default rules

We don't use the default implicit rules that are added by make, so
they just slow down the Makefile processing. The default implicit
rules can be removed by defining an empty .SUFFIXES: target.

This speeds up the start of the build on my machine from 5.6s to
4.9s.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

Makefile

@@ -24,6 +24,9 @@
 # You shouldn't need to mess with anything beyond this point...
 #--------------------------------------------------------------
 
+# Delete default rules. We don't use them. This saves a bit of time.
+.SUFFIXES:
+
 # we want bash as shell
 SHELL := $(shell if [ -x "$$BASH" ]; then echo $$BASH; \
 	 else if [ -x /bin/bash ]; then echo /bin/bash; \