Added possibility to specify cmake build folder

This is useful to compile all tests for different tile sizes and
then run all the tests to be able to run them in parallel.

Author: haugoug

Makefile

@@ -20,6 +20,7 @@
 
 SHELL 			:= /bin/bash
 
+CMAKE_BUILDDIR  	?= build
 BUILD_DIR 		?= ../sw/tests/$(test)
 MAGIA_DIR 		?= ../
 GVSOC_DIR 		?= ./gvsoc
@@ -39,7 +40,7 @@ tiles_2 		:= $(shell echo $$(( $(tiles) * $(tiles) )))
 tiles_log    	:= $(shell awk 'BEGIN { printf "%.0f", log($(tiles_2))/log(2) }')
 tiles_log_real  := $(shell awk 'BEGIN { printf "%.0f", log($(tiles))/log(2) }')
 
-.PHONY: gvsoc
+.PHONY: gvsoc build
 
 clean:
 	rm -rf build/
@@ -66,8 +67,8 @@ ifeq ($(compiler), GCC_MULTILIB)
 	sed -i -E 's/^#add_subdirectory\(flatatt\)/add_subdirectory\(flatatt\)/' ./tests/magia/mesh/CMakeLists.txt
 	sed -i -E 's/^\/\/#include "utils\/attention_utils.h"/#include "utils\/attention_utils.h"/' ./targets/magia/include/tile.h
 endif
-	cmake -DTARGET_PLATFORM=$(target_platform) -DEVAL=$(eval) -DCOMPILER=$(compiler) -B build --trace-expand
-	cmake --build build --verbose
+	cmake -DTARGET_PLATFORM=$(target_platform) -DEVAL=$(eval) -DCOMPILER=$(compiler) -B $(CMAKE_BUILDDIR) --trace-expand
+	cmake --build $(CMAKE_BUILDDIR) --verbose
 
 set_mesh:
 ifeq ($(tiles), 1)