Add a way to track all dlsym calls

Add dlsym option to debug.ld.all and debug.ld.app.<appname> which
enables logging of dlsym calls.

Bug: http://b/29458203
Test: flash, set debug.ld.all to dlsym and check
      if there are messages in logcat

Change-Id: I9cb815a38b5b98aac9ebe3ac1540bcdedd2e8db0
diff --git a/linker/linker_logger.h b/linker/linker_logger.h
index 0932471..502f872 100644
--- a/linker/linker_logger.h
+++ b/linker/linker_logger.h
@@ -40,6 +40,7 @@
 
 constexpr const uint32_t kLogErrors = 1 << 0;
 constexpr const uint32_t kLogDlopen = 1 << 1;
+constexpr const uint32_t kLogDlsym  = 1 << 2;
 
 class LinkerLogger {
  public: