Unbreak the bootstrap lib build on MinGW

With -std=c++0x, MinGW headers doesn't declare some common functions
we're using in qglobal.cpp.

Change-Id: I0ba68ee73b1099c8591a578f06f58db316631e8e
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/tools/bootstrap/bootstrap.pro

@@ -5,6 +5,9 @@ QT =
 CONFIG += no_module_headers internal_module
 !build_pass: CONFIG += release
 
+# otherwise mingw headers do not declare common functions like putenv
+win32-g++*:QMAKE_CXXFLAGS_CXX11 = -std=gnu++0x
+
 MODULE_DEFINES = \
         QT_BOOTSTRAPPED \
         QT_LITE_UNICODE \