Add support for constructing a t?csh environment (#370)

emsdk_env.csh

@@ -0,0 +1,36 @@
+# This script is sourced by the user and uses
+# their shell. Try not to use tcshisms.
+
+# Do not execute this script without sourcing,
+# because it won't have any effect then.
+# That is, always run this script with
+#
+#     . ./emsdk_env.csh
+# or
+#     source ./emsdk_env.csh
+#
+# instead of just plainly running with
+#
+#     ./emsdk_env.csh
+#
+# which won't have any effect.
+set SRC=($_)
+if ("$SRC" == "") then
+  set SRC="$0"
+else
+  set SRC="$SRC[2]"
+endif
+set CURDIR=`pwd`
+cd `dirname "$SRC"`
+unset SRC
+
+setenv EMSDK_CSH 1
+
+set tmpfile=`mktemp` || exit 1
+./emsdk construct_env $tmpfile
+source $tmpfile
+rm -f $tmpfile
+
+unsetenv EMSDK_CSH
+
+cd "$CURDIR"