Allow to disable Stacktrace support

Enable backtrace stuff only if GNU C library used, because current
backtrace implementation based  on  <execinfo.h> , which is not a
part of standard C library, it is a GNU extension.

This will be usefull when building  with  custom POSIX-compilant C
library (like musl) and no <execinfo.h> available.

Note: configure script will detect presence of  <execinfo.h>  and
enable/disable feature depending on it.

Feature is enabled by default.

src/src.pro

@@ -33,13 +33,17 @@ nogui {
         LIBS += -lobjc
     }
 }
+
 nowebui {
     DEFINES += DISABLE_WEBUI
 }
-strace_win {
-    DEFINES += STACKTRACE_WIN
-    DEFINES += STACKTRACE_WIN_PROJECT_PATH=$$PWD
-    DEFINES += STACKTRACE_WIN_MAKEFILE_PATH=$$OUT_PWD
+
+stacktrace {
+    DEFINES += STACKTRACE
+    win32 {
+        DEFINES += STACKTRACE_WIN_PROJECT_PATH=$$PWD
+        DEFINES += STACKTRACE_WIN_MAKEFILE_PATH=$$OUT_PWD
+    }
 }
 
 CONFIG(debug, debug|release): message(Project is built in DEBUG mode.)