make [all] now uses the guix build environment (but other targets don't)

.travis.yml

@@ -3,6 +3,7 @@ language: c
 addons:
   apt:
     packages: &common_apt_packages
+      - guix
       # graphical environment
       - scrot
       - twm

Makefile

@@ -20,6 +20,11 @@ tests_emu = test/qemu-system-i386-floppy test/qemu-system-i386-cdrom test/qemu-s
 tests_requiring_sudo = test/fat12_mount test/iso_mount
 tests_noemu = test/zip test/os.reasm test/sizes test/fat12_contents test/reproducible_build
 
+.DEFAULT_GOAL := all
+.PHONY: all
+all:
+	cp -f "$$(guix build --check -f guix.scm)/bin/$$(basename "${os_filename}")" "${os_filename}"
+
 # We truncate the timezone, because the Darwin version of date seems to lack
 # the %:z format (for ±HH:MM timezone).
 define date_command
@@ -52,9 +57,9 @@ include Makefile.test-example-os
 
 more_built_directories = ${built_directories} ${bld}
 
-.PHONY: all
-# all: os.arm.disasm
-all: .gitignore \
+.PHONY: in-guix
+# in-guix: os.arm.disasm
+in-guix: .gitignore \
          ${bld}/check_makefile
 
 ${bld}/makefile_w_arnings: | $${@D}

Makefile.example-os

@@ -73,7 +73,7 @@ os_partition_size_sectors = 717 # 720 - start
 os_floppy_chs_h = 2
 os_floppy_chs_s = 9
 
-all: ${os_filename} \
+in-guix: ${os_filename} \
          ${bld}/os.ndisasm.disasm \
          ${bld}/os.reasm.asm \
          ${bld}/os.file \

guix.scm

@@ -81,7 +81,7 @@
         (delete 'patch-shebangs)
         (delete 'strip))
       #:parallel-build? #t
-      #:make-flags '("COMMIT_TIMESTAMP_ISO_8601=1970-01-01T00:00:00+00:00")))
+      #:make-flags '("in-guix" "COMMIT_TIMESTAMP_ISO_8601=1970-01-01T00:00:00+00:00")))
    (native-inputs
     `(("nasm" ,nasm)
       ("which" ,which)