qtbase: disable gdb_dwarf_index

* qmake is trying to call native gdb and we don't depend on gdb-native
  (or even provide gdb-native)
* fixes errors like this:
  /bin/sh: gdb: command not found
  /bin/sh: line 0: test: -gt: unary operator expected
  which are not fatal, but still misleading in do_configure output

recipes-qt/qt5/qtbase/qmake.conf

@@ -3,7 +3,7 @@
 #
 
 MAKEFILE_GENERATOR	= UNIX
-CONFIG += incremental gdb_dwarf_index
+CONFIG += incremental
 QMAKE_INCREMENTAL_STYLE = sublib
 
 include(../common/linux.conf)