Makefile: sort unexport lines

The list of environment variables to unexport has grown organically over the
years and is no longer sorted. Sort it alphabetically for clarity.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>
(cherry picked from commit da04cfa26ce7da042c40caa94252c566f47a070c)
Signed-off-by: Thomas Perale <thomas.perale@mind.be>

Makefile

@@ -407,27 +407,27 @@ ifeq ($(BR2_HAVE_DOT_CONFIG),y)
 # Hide troublesome environment variables from sub processes
 #
 ################################################################################
-unexport CROSS_COMPILE
+unexport AR
 unexport ARCH
 unexport CC
-unexport LD
-unexport AR
-unexport CXX
-unexport CPP
-unexport RANLIB
 unexport CFLAGS
+unexport CONFIG_SITE
+unexport CPP
+unexport CROSS_COMPILE
+unexport CXX
 unexport CXXFLAGS
+unexport DEVICE_TREE
+unexport GCC_COLORS
 unexport GREP_OPTIONS
-unexport TAR_OPTIONS
-unexport CONFIG_SITE
-unexport QMAKESPEC
-unexport TERMINFO
+unexport LD
 unexport MACHINE
 unexport O
-unexport GCC_COLORS
-unexport PLATFORM
 unexport OS
-unexport DEVICE_TREE
+unexport PLATFORM
+unexport QMAKESPEC
+unexport RANLIB
+unexport TAR_OPTIONS
+unexport TERMINFO
 
 GNU_HOST_NAME := $(shell support/gnuconfig/config.guess)