use environment variables

Common/base.pri

@@ -155,6 +155,12 @@ core_windows {
 
 DEFINES += CRYPTOPP_DISABLE_ASM
 }
+
+# use environment variables
+QMAKE_CFLAGS += $$(CFLAGS)
+QMAKE_CXXFLAGS += $$(CXXFLAGS)
+QMAKE_LFLAGS += $$(LDFLAGS)
+
 !use_curl {
     DEFINES += DISABLE_FILE_DOWNLOADER
 }