Add unsupported option to install-build-deps.

build/install-build-deps.sh

Index: build/install-build-deps.sh
diff --git a/build/install-build-deps.sh b/build/install-build-deps.sh
index 4d104519083fcfdd18e80763898ef754c68163d0..c891f2709da576de67628f3796bb3e3a72d2873a 100755
--- a/build/install-build-deps.sh
+++ b/build/install-build-deps.sh
@@ -31,6 +31,7 @@ do
   --no-prompt)              do_default=1
                             do_quietly="-qq --assume-yes"
     ;;
+  --unsupported)            do_unsupported=1;;
   *) usage;;
   esac
   shift
@@ -38,16 +39,23 @@ done
 
 ubuntu_versions="10\.04|10\.10|11\.04|11\.10|12\.04|12\.10"
 ubuntu_codenames="lucid|maverick|natty|oneiric|precise|quantal"
+ubuntu_issue="Ubuntu ($ubuntu_versions|$ubuntu_codenames)"
+# GCEL is an Ubuntu-derived VM image used on Google Compute Engine; /etc/issue
+# doesn't contain a version number so just trust that the user knows what
+# they're doing.
+gcel_issue="^GCEL"
+
+if [ 0 -eq "${do_unsupported-0}" ] ; then
+  if ! egrep -q "($ubuntu_issue|$gcel_issue)" /etc/issue; then
+    echo "ERROR: Only Ubuntu 10.04 (lucid) through 12.10 (quantal) are"\
+        "currently supported" >&2
+    exit 1
+  fi
 
-if ! egrep -q "Ubuntu ($ubuntu_versions|$ubuntu_codenames)" /etc/issue; then
-  echo "ERROR: Only Ubuntu 10.04 (lucid) through 12.10 (quantal) are currently"\
-      "supported" >&2
-  exit 1
-fi
-
-if ! uname -m | egrep -q "i686|x86_64"; then
-  echo "Only x86 architectures are currently supported" >&2
-  exit
+  if ! uname -m | egrep -q "i686|x86_64"; then
+    echo "Only x86 architectures are currently supported" >&2
+    exit
+  fi
 fi
 
 if [ "x$(id -u)" != x0 ]; then