src: mv ../buildEnvironmentVariables mkhdr

Also note that the file must be valid shell and mk input.
For #321.

dist/buildmk

@@ -1,6 +1,6 @@
 #!/bin/sh
 
 # run this in the src directory
+. ../src/mkenv
 export SYSNAME OBJTYPE
-. ../buildEnvironmentVariables
 sh -x mkmk.sh

src/mkenv

@@ -1,3 +1,6 @@
+# This file must be valid mk input for mkhdr
+# and also valid shell input for ../dist/buildmk
+
 SYSNAME=`uname`
 OBJTYPE=`(uname -m -p 2>/dev/null || uname -m) | sed '
 	s;.*i[3-6]86.*;386;;

src/mkhdr

@@ -1,4 +1,4 @@
-<$PLAN9/buildEnvironmentVariables
+<$PLAN9/src/mkenv
 
 BIN=$PLAN9/bin
 LIBDIR=$PLAN9/lib