Make GetSourceVersion more portable, thanks Pawel!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94186 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/GetSourceVersion b/utils/GetSourceVersion
index 63cfe0f..b25f2f9 100755
--- a/utils/GetSourceVersion
+++ b/utils/GetSourceVersion
@@ -1,6 +1,6 @@
 #!/bin/sh
 
-function usage() {
+usage() {
    echo "usage: $0 <source root>"
    echo "  Prints the source control revision of the given source directory,"
    echo "  the exact format of the revision string depends on the source "