Add a tool for generating amalgamated builds

This patch adds tools/gen_amalgamated, which can take a number of GN
targets and produce an "amalgamated" header and source file pair. These
can be more easily incorporated to various build systems where GN isn't
readily available.

We also fix a few naming collisions that prevented the amalgamated build
from succeeding.

Test:
  $ (cd buildtools/protobuf; ./configure && make)
  $ tools/gen_amalgamated --build

Example output: https://drive.google.com/open?id=12HPn02Cscv5-eCW9MSoNpfNjS2y0pgSv

Change-Id: Idb894713e8283d5ee2dc46c5eb7bbb291e4185ba
diff --git a/src/traced/probes/probes_producer.cc b/src/traced/probes/probes_producer.cc
index afe2ded..202fadc 100644
--- a/src/traced/probes/probes_producer.cc
+++ b/src/traced/probes/probes_producer.cc
@@ -53,7 +53,7 @@
 constexpr uint32_t kInitialConnectionBackoffMs = 100;
 constexpr uint32_t kMaxConnectionBackoffMs = 30 * 1000;
 
-// Should be larger than FtraceController::kFlushTimeoutMs.
+// Should be larger than FtraceController::kControllerFlushTimeoutMs.
 constexpr uint32_t kFlushTimeoutMs = 1000;
 
 constexpr char kFtraceSourceName[] = "linux.ftrace";