qt4: 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

---
 meta/recipes-qt/qt4/qt4-4.8.4/g++.conf | 3 +++
 1 file changed, 3 insertions(+)

index e58fb15..d34c62c 100644
@@ -49,6 +49,9 @@ QMAKE_PCH_OUTPUT_EXT    = .gch
 QMAKE_LFLAGS_BSYMBOLIC_FUNC = -Wl,-Bsymbolic-functions
 QMAKE_LFLAGS_DYNAMIC_LIST = -Wl,--dynamic-list,
 
+# do not depend on gdb
+CONFIG -= gdb_dwarf_index
+
 # some linking helper...
 CONFIG += rpath_libdirs
 

1.8.3