Moved build artifacts into root build folder

The intermediate files used for build (.o, .a ...) are still
in subfolders to avoid conflicts.

Fix #3807

Author: cmaglie

platform.txt

@@ -75,17 +75,17 @@ recipe.S.o.pattern="{compiler.path}{compiler.S.cmd}" {compiler.S.flags} -mcpu={b
 recipe.ar.pattern="{compiler.path}{compiler.ar.cmd}" {compiler.ar.flags} {compiler.ar.extra_flags} "{build.path}/{archive_file}" "{object_file}"
 
 ## Combine gc-sections, archives, and objects
-recipe.c.combine.pattern="{compiler.path}{compiler.c.elf.cmd}" {compiler.c.elf.flags} -mcpu={build.mcu} "-T{build.variant.path}/{build.ldscript}" "-Wl,-Map,{build.path}/sketch/{build.project_name}.map" {compiler.c.elf.extra_flags} -o "{build.path}/sketch/{build.project_name}.elf" "-L{build.path}" -mthumb -Wl,--cref -Wl,--check-sections -Wl,--gc-sections -Wl,--entry=Reset_Handler -Wl,--unresolved-symbols=report-all -Wl,--warn-common -Wl,--warn-section-align -Wl,--warn-unresolved-symbols -Wl,--start-group "{build.path}/core/syscalls_sam3.c.o" {object_files} "{build.variant.path}/{build.variant_system_lib}" "{build.path}/{archive_file}" -Wl,--end-group -lm -gcc
+recipe.c.combine.pattern="{compiler.path}{compiler.c.elf.cmd}" {compiler.c.elf.flags} -mcpu={build.mcu} "-T{build.variant.path}/{build.ldscript}" "-Wl,-Map,{build.path}/{build.project_name}.map" {compiler.c.elf.extra_flags} -o "{build.path}/{build.project_name}.elf" "-L{build.path}" -mthumb -Wl,--cref -Wl,--check-sections -Wl,--gc-sections -Wl,--entry=Reset_Handler -Wl,--unresolved-symbols=report-all -Wl,--warn-common -Wl,--warn-section-align -Wl,--warn-unresolved-symbols -Wl,--start-group "{build.path}/core/syscalls_sam3.c.o" {object_files} "{build.variant.path}/{build.variant_system_lib}" "{build.path}/{archive_file}" -Wl,--end-group -lm -gcc
 
 ## Create output (.bin file)
-recipe.objcopy.bin.pattern="{compiler.path}{compiler.elf2hex.cmd}" {compiler.elf2hex.flags} {compiler.elf2hex.extra_flags} "{build.path}/sketch/{build.project_name}.elf" "{build.path}/sketch/{build.project_name}.bin"
+recipe.objcopy.bin.pattern="{compiler.path}{compiler.elf2hex.cmd}" {compiler.elf2hex.flags} {compiler.elf2hex.extra_flags} "{build.path}/{build.project_name}.elf" "{build.path}/{build.project_name}.bin"
 
 ## Save hex
 recipe.output.tmp_file={build.project_name}.bin
 recipe.output.save_file={build.project_name}.{build.variant}.bin
 
 ## Compute size
-recipe.size.pattern="{compiler.path}{compiler.size.cmd}" -A "{build.path}/sketch/{build.project_name}.elf"
+recipe.size.pattern="{compiler.path}{compiler.size.cmd}" -A "{build.path}/{build.project_name}.elf"
 recipe.size.regex=\.text\s+([0-9]+).*
 
 
@@ -98,5 +98,5 @@ tools.bossac.cmd.windows=bossac.exe
 
 tools.bossac.upload.params.verbose=-i -d
 tools.bossac.upload.params.quiet=
-tools.bossac.upload.pattern="{path}/{cmd}" {upload.verbose} --port={serial.port.file} -U {upload.native_usb} -e -w -v -b "{build.path}/sketch/{build.project_name}.bin" -R
+tools.bossac.upload.pattern="{path}/{cmd}" {upload.verbose} --port={serial.port.file} -U {upload.native_usb} -e -w -v -b "{build.path}/{build.project_name}.bin" -R