Fixup multibuild filegen (#16166)

* Add env variable support to multibuild.

* Generate version.h in build-specific location.

build_keyboard.mk

@@ -44,7 +44,6 @@ endif
 ifdef SKIP_GIT
 VERSION_H_FLAGS := --skip-git
 endif
-$(shell $(QMK_BIN) generate-version-h $(VERSION_H_FLAGS) -q -o quantum/version.h)
 
 # Determine which subfolders exist.
 KEYBOARD_FOLDER_PATH_1 := $(KEYBOARD)
@@ -166,6 +165,11 @@ generated-files: $(KEYMAP_OUTPUT)/src/config.h $(KEYMAP_OUTPUT)/src/keymap.c
 
 endif
 
+generated-files: $(KEYMAP_OUTPUT)/src/version.h
+$(KEYMAP_OUTPUT)/src/version.h:
+	[ -d $(KEYMAP_OUTPUT)/src ] || mkdir -p $(KEYMAP_OUTPUT)/src
+	$(QMK_BIN) generate-version-h $(VERSION_H_FLAGS) -q -o $(KEYMAP_OUTPUT)/src/version.h
+
 ifeq ($(strip $(CTPC)), yes)
   CONVERT_TO_PROTON_C=yes
 endif
@@ -393,6 +397,7 @@ VPATH += $(KEYMAP_PATH)
 VPATH += $(USER_PATH)
 VPATH += $(KEYBOARD_PATHS)
 VPATH += $(COMMON_VPATH)
+VPATH += $(KEYMAP_OUTPUT)/src
 
 include common_features.mk
 include $(BUILDDEFS_PATH)/generic_features.mk

lib/python/qmk/cli/multibuild.py

@@ -32,6 +32,7 @@ def _is_split(keyboard_name):
 @cli.argument('-c', '--clean', arg_only=True, action='store_true', help="Remove object files before compiling.")
 @cli.argument('-f', '--filter', arg_only=True, action='append', default=[], help="Filter the list of keyboards based on the supplied value in rules.mk. Supported format is 'SPLIT_KEYBOARD=yes'. May be passed multiple times.")
 @cli.argument('-km', '--keymap', type=str, default='default', help="The keymap name to build. Default is 'default'.")
+@cli.argument('-e', '--env', arg_only=True, action='append', default=[], help="Set a variable to be passed to make. May be passed multiple times.")
 @cli.subcommand('Compile QMK Firmware for all keyboards.', hidden=False if cli.config.user.developer else True)
 def multibuild(cli):
     """Compile QMK Firmware against all keyboards.
@@ -68,7 +69,7 @@ def multibuild(cli):
 all: {keyboard_safe}_binary
 {keyboard_safe}_binary:
 	@rm -f "{QMK_FIRMWARE}/.build/failed.log.{keyboard_safe}" || true
-	+@$(MAKE) -C "{QMK_FIRMWARE}" -f "{QMK_FIRMWARE}/build_keyboard.mk" KEYBOARD="{keyboard_name}" KEYMAP="{cli.args.keymap}" REQUIRE_PLATFORM_KEY= COLOR=true SILENT=false \\
+	+@$(MAKE) -C "{QMK_FIRMWARE}" -f "{QMK_FIRMWARE}/build_keyboard.mk" KEYBOARD="{keyboard_name}" KEYMAP="{cli.args.keymap}" REQUIRE_PLATFORM_KEY= COLOR=true SILENT=false {' '.join(cli.args.env)} \\
 		>>"{QMK_FIRMWARE}/.build/build.log.{os.getpid()}.{keyboard_safe}" 2>&1 \\
 		|| cp "{QMK_FIRMWARE}/.build/build.log.{os.getpid()}.{keyboard_safe}" "{QMK_FIRMWARE}/.build/failed.log.{os.getpid()}.{keyboard_safe}"
 	@{{ grep '\[ERRORS\]' "{QMK_FIRMWARE}/.build/build.log.{os.getpid()}.{keyboard_safe}" >/dev/null 2>&1 && printf "Build %-64s \e[1;31m[ERRORS]\e[0m\\n" "{keyboard_name}:{cli.args.keymap}" ; }} \\