[LLGS] Avoid misrepresenting log lines as inferior output

Summary:
in case we are logging to stdout, any log lines from the forked child can be misconstrued to be
inferior output. To avoid this, we disable all logging immediately after forking.

I also fix the implementatoion of DisableAllLogChannels, which was a no-op before this commit.

Reviewers: clayborg, ovyalov

Subscribers: dean, lldb-commits

Differential Revision: http://reviews.llvm.org/D12083

llvm-svn: 245272
diff --git a/lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp b/lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp
index b4afe62..b237339 100644
--- a/lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp
+++ b/lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp
@@ -560,8 +560,11 @@
     // Child process.
     if (pid == 0)
     {
+        // First, make sure we disable all logging. If we are logging to stdout, our logs can be
+        // mistaken for inferior output.
+        Log::DisableAllLogChannels(nullptr);
         // FIXME consider opening a pipe between parent/child and have this forked child
-        // send log info to parent re: launch status, in place of the log lines removed here.
+        // send log info to parent re: launch status.
 
         // Start tracing this child that is about to exec.
         error = PtraceWrapper(PTRACE_TRACEME, 0);