Bitcoin-Qt (Windows only): add ASLR and DEP linker flags

- for extra security on Windows: enable ASLR and DEP via GCC linker flags

GCC linker flag description:
--dynamicbase  The image base address may be relocated using address space layout randomization (ASLR). This feature was introduced with MS Windows Vista for i386 PE targets.
--nxcompat The image is compatible with the Data Execution Prevention.
This feature was introduced with MS Windows XP SP2 for i386 PE targets.

bitcoin-qt.pro

@@ -30,6 +30,9 @@ contains(RELEASE, 1) {
     }
 }
 
+# for extra security on Windows: enable ASLR and DEP via GCC linker flags
+win32:QMAKE_LFLAGS *= -Wl,--dynamicbase -Wl,--nxcompat
+
 # use: qmake "USE_QRCODE=1"
 # libqrencode (http://fukuchi.org/works/qrencode/index.en.html) must be installed for support
 contains(USE_QRCODE, 1) {