Doc: Describe new GDB options

Task-number: QTCREATORBUG-25642
Change-Id: I32b5d9bffd0eab2dbc1f6afd1f05be149fe1a10e
Reviewed-by: hjk <hjk@qt.io>

doc/qtcreator/src/debugger/creator-debugger-common.qdocinc

@@ -162,6 +162,10 @@
     editor, select \uicontrol GDB > \uicontrol {Adjust breakpoint locations}
     or \uicontrol CDB > \uicontrol {Correct breakpoint location}.
 
+    When using GDB as backend, you can extend the ordinary GDB
+    breakpoint class by using Python. Select \uicontrol GDB >
+    \uicontrol {Use pseudo message tracepoints}.
+
     When using CDB as backend, you can specify that the debugger should break on
     specific events, such as C++ exceptions, thread creation or exit, loading or
     unloading \l{Viewing Modules}{application modules}, or particular output.

doc/qtcreator/src/debugger/creator-only/creator-debugger-settings.qdocinc

@@ -112,6 +112,10 @@
     By default, GDB shows AT&T style disassembly. To switch to the Intel style,
     select the \uicontrol {Use Intel style disassembly} check box.
 
+    To have GDB automatically save a copy of its symbol index in a cache
+    on disk and retrieve it from there when loading the same binary in the
+    future, select the \uicontrol {Use automatic symbol cache} check box.
+
     To execute GDB commands after GDB has been started, but before the debugged
     program is started or attached, and before the debugging helpers are
     initialized, enter them in the \uicontrol {Additional Startup Commands}

doc/qtcreator/src/debugger/creator-only/creator-debugger.qdoc

@@ -1540,8 +1540,16 @@
 
     \section1 Built-in Debugger Is Slow During Startup and Runtime
 
-    The part of the slowness that is related to the loading of debug information
-    is hard to avoid. Another part stems from maintaining breakpoints inside
+    Slowness that is related to the loading of debug information is hard to
+    avoid.
+
+    When using GDB as backend, you can automatically save a copy of
+    its symbol index in a cache on disk and retrieve it from there
+    when loading the same binary in the future. Select \uicontrol Tools
+    > \uicontrol Options > \uicontrol Debugger > \uicontrol GDB >
+    \uicontrol {Use automatic symbol cache}.
+
+    Some slowness stems from maintaining breakpoints inside
     the debugger (under some circumstances all breakpoints need to be inserted
     and removed again for each step) and the evaluation of expressions after
     each step. We recommend that you minimize the number of breakpoints and