[scons] Allow setting compiler optimization level.

The optimization level can be set in `project.cfg` as
`build.optimization=level` and overwritten using the command line 
argument `optimization=level`.

scons/site_tools/arm.py

@@ -124,7 +124,7 @@ def generate(env, **kw):
 		"$FPU",
 		"$THUMB",			# use THUMB='-mthumb' to compile as thumb code (default for AT91SAM)
 		"-mthumb-interwork",
-		"-Os",
+		"$OPTIMIZATION",
 		"-gdwarf-2",
 		"-funsigned-char",
 		"-funsigned-bitfields",

scons/site_tools/avr.py

@@ -121,7 +121,7 @@ def generate(env, **kw):
 	# flags for C and C++
 	env['CCFLAGS'] = [
 		"-mmcu=$AVR_DEVICE", 
-		"-Os",
+		"$OPTIMIZATION",
 		"-gdwarf-2", 
 		"-funsigned-char",
 		"-funsigned-bitfields", 

scons/site_tools/hosted.py

@@ -89,6 +89,7 @@ def generate(env, **kw):
 		"-Wundef",
 		"-ggdb",
 		"-DBASENAME=${SOURCE.file}",
+		"$OPTIMIZATION",
 	]
 
 	#if c_compiler == 'clang':

scons/site_tools/xpcc.py

@@ -354,6 +354,11 @@ def generate(env, **kw):
 		if buildpath is None:
 			buildpath = parser.get('build', 'buildpath', os.path.join(os.curdir, 'build/'))
 
+		# optimization level can be declared in project.cfg
+		optimization = parser.get('build', 'optimization', 's')
+		# but can be overwritten by command line
+		optimization = ARGUMENTS.get('optimization', optimization)
+
 		# load parameters if available
 		if parser.has_section('parameters'):
 			env['XPCC_USER_PARAMETERS'] = parser.items('parameters')
@@ -388,6 +393,15 @@ def generate(env, **kw):
 	env['XPCC_SYSTEM_BUILDER'] = os.path.join(rootpath, 'tools', 'system_design', 'builder')
 	env['XPCC_DEVICE'] = device 			# needed by the platform tools
 
+	# compiler optimization
+	optimization_levels = ['0', '1', '2', '3', 's']
+	if optimization in optimization_levels:
+		env['OPTIMIZATION'] = "-O{}".format(optimization)
+	else:
+		env.Error("scons: Unknown compiler optimization level '{}'!".format(optimization))
+		env.Error("Available optimization levels are [{}]".format(', '.join(optimization_levels)))
+		Exit(1)
+
 	# tools which are used independently of the architecture
 	env.Tool('template') # needs to be added before platform_tools
 	env.Tool('unittest')