[gnome-terminal] build: Treat precious variables correctly

[Christian Persch <chpe src gnome org>]

commit 43bc7b5f2f23b9937f0e74aa51bb0c14e9cb686b
Author: Christian Persch <chpe gnome org>
Date:   Sun Apr 24 13:17:42 2016 +0200

    build: Treat precious variables correctly
    
    Test if a precious variable is set already before overwriting it.

 configure.ac |   36 ++++++++++++++++++++++++------------
 1 files changed, 24 insertions(+), 12 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 6606976..701aebf 100644
--- a/configure.ac
+++ b/configure.ac
@@ -187,39 +187,51 @@ AM_CONDITIONAL([ENABLE_MIGRATION],[test "$enable_migration" = "yes"])
 # ***********
 
 AC_ARG_VAR([GLIB_GENMARSHAL],[the glib-genmarschal programme])
-AC_PATH_PROG([GLIB_GENMARSHAL],[glib-genmarshal],[])
 if test -z "$GLIB_GENMARSHAL"; then
-  AC_MSG_ERROR([glib-genmarshal not found])
+  AC_PATH_PROG([GLIB_GENMARSHAL],[glib-genmarshal],[])
+  if test -z "$GLIB_GENMARSHAL"; then
+    AC_MSG_ERROR([glib-genmarshal not found])
+  fi
 fi
 
 AC_ARG_VAR([GLIB_MKENUMS],[the glib-mkenums programme])
-AC_PATH_PROG([GLIB_MKENUMS],[glib-mkenums],[])
 if test -z "$GLIB_MKENUMS"; then
-  AC_MSG_ERROR([glib-mkenums not found])
+  AC_PATH_PROG([GLIB_MKENUMS],[glib-mkenums],[])
+  if test -z "$GLIB_MKENUMS"; then
+    AC_MSG_ERROR([glib-mkenums not found])
+  fi
 fi
 
 AC_ARG_VAR([GLIB_COMPILE_RESOURCES],[the glib-compile-resources programme])
-AC_PATH_PROG([GLIB_COMPILE_RESOURCES],[glib-compile-resources],[])
 if test -z "$GLIB_COMPILE_RESOURCES"; then
-  AC_MSG_ERROR([glib-compile-resources not found])
+  AC_PATH_PROG([GLIB_COMPILE_RESOURCES],[glib-compile-resources],[])
+  if test -z "$GLIB_COMPILE_RESOURCES"; then
+    AC_MSG_ERROR([glib-compile-resources not found])
+  fi
 fi
 
 AC_ARG_VAR([GDBUS_CODEGEN],[the gdbus-codegen programme])
-AC_PATH_PROG([GDBUS_CODEGEN],[gdbus-codegen],[])
 if test -z "$GDBUS_CODEGEN"; then
-  AC_MSG_ERROR([gdbus-codegen not found])
+  AC_PATH_PROG([GDBUS_CODEGEN],[gdbus-codegen],[])
+  if test -z "$GDBUS_CODEGEN"; then
+    AC_MSG_ERROR([gdbus-codegen not found])
+  fi
 fi
 
 AC_ARG_VAR([XMLLINT],[the xmllint programme])
-AC_PATH_PROG([XMLLINT],[xmllint],[])
 if test -z "$XMLLINT"; then
-  AC_MSG_ERROR([xmllint not found])
+  AC_PATH_PROG([XMLLINT],[xmllint],[])
+  if test -z "$XMLLINT"; then
+    AC_MSG_ERROR([xmllint not found])
+  fi
 fi
 
 AC_ARG_VAR([DESKTOP_FILE_VALIDATE],[the desktop-file-validate programme])
-AC_PATH_PROG([DESKTOP_FILE_VALIDATE],[desktop-file-validate],[])
 if test -z "$DESKTOP_FILE_VALIDATE"; then
-  AC_MSG_ERROR([desktop-file-validate not found])
+  AC_PATH_PROG([DESKTOP_FILE_VALIDATE],[desktop-file-validate],[])
+  if test -z "$DESKTOP_FILE_VALIDATE"; then
+    AC_MSG_ERROR([desktop-file-validate not found])
+  fi
 fi
 
 # ***************************