Suppress -Wcomment compiler warnings
Suppress -Wcomment compiler warnings

We have a bunch of annoying warnings in otherwise-normal g++ builds.
Let's get rid of these unnecessary warnings. Examples:

  [765/1328] Building CXX object src/kudu/util/CMakeFiles/interval_tree-test.dir/interval_tree-test.cc.o
  In file included from ../../src/kudu/util/interval_tree-test.cc:37:0:
  ../../src/kudu/util/interval_tree-inl.h:269:3: warning: multi-line comment [-Wcomment]
    //   [------]         \
    ^
  ../../src/kudu/util/interval_tree-inl.h:308:3: warning: multi-line comment [-Wcomment]
    //     [--------]   \
    ^
  [943/1328] Building CXX object src/kudu/server/CMakeFiles/server_process.dir/webserver.cc.o
  ../../src/kudu/server/webserver.cc:360:5: warning: multi-line comment [-Wcomment]
      // https://github.com/cloudera/squeasel/blob/\
      ^
  [995/1328] Building CXX object src/kudu/tablet/CMakeFiles/tablet.dir/rowset_tree.cc.o
  In file included from ../../src/kudu/tablet/rowset_tree.cc:33:0:
  ../../src/kudu/util/interval_tree-inl.h:269:3: warning: multi-line comment [-Wcomment]
    //   [------]         \
    ^
  ../../src/kudu/util/interval_tree-inl.h:308:3: warning: multi-line comment [-Wcomment]
    //     [--------]   \
    ^
  [1218/1328] Building CXX object src/kudu/tools/CMakeFiles/kudu.dir/tool_action_perf.cc.o
  ../../src/kudu/tools/tool_action_perf.cc:33:1: warning: multi-line comment [-Wcomment]
  //   kudu perf loadgen \
  ^
  ../../src/kudu/tools/tool_action_perf.cc:49:1: warning: multi-line comment [-Wcomment]
  //   kudu perf loadgen \
  ^
  ../../src/kudu/tools/tool_action_perf.cc:65:1: warning: multi-line comment [-Wcomment]
  //   kudu perf loadgen \
  ^
  ../../src/kudu/tools/tool_action_perf.cc:82:1: warning: multi-line comment [-Wcomment]
  //   kudu perf loadgen \
  ^
  ../../src/kudu/tools/tool_action_perf.cc:94:1: warning: multi-line comment [-Wcomment]
  //   kudu perf loadgen 127.0.0.1 --table_name=t3 --num_threads=2 \
  ^
  ../../src/kudu/tools/tool_action_perf.cc:97:1: warning: multi-line comment [-Wcomment]
  //   kudu perf loadgen 127.0.0.1 --table_name=t3 --num_threads=2 \
  ^
  ../../src/kudu/tools/tool_action_perf.cc:100:1: warning: multi-line comment [-Wcomment]
  //   perf perf loadgen 127.0.0.1 --table_name=t3 --num_threads=2 \
  ^

Change-Id: Ic320fa11a6f67ed107b1fff2b1f2da7f7bd39cd0
Reviewed-on: http://gerrit.cloudera.org:8080/8495
Reviewed-by: Alexey Serbin <864f6b82bd94e8dda64141d4274519ee66e0102e@cloudera.com>
Tested-by: Kudu Jenkins

andrwng/kudu,helifu/kudu,InspurUSA/kudu,andrwng/kudu,cloudera/kudu,andrwng/kudu,cloudera/kudu,andrwng/kudu,cloudera/kudu,helifu/kudu,andrwng/kudu,EvilMcJerkface/kudu,helifu/kudu,InspurUSA/kudu,cloudera/kudu,InspurUSA/kudu,andrwng/kudu,InspurUSA/kudu,helifu/kudu,InspurUSA/kudu,EvilMcJerkface/kudu,EvilMcJerkface/kudu,helifu/kudu,InspurUSA/kudu,cloudera/kudu,EvilMcJerkface/kudu,cloudera/kudu,EvilMcJerkface/kudu,andrwng/kudu,andrwng/kudu,andrwng/kudu,EvilMcJerkface/kudu,cloudera/kudu,EvilMcJerkface/kudu,InspurUSA/kudu,InspurUSA/kudu,helifu/kudu,InspurUSA/kudu,helifu/kudu,EvilMcJerkface/kudu,EvilMcJerkface/kudu,cloudera/kudu,cloudera/kudu,helifu/kudu,helifu/kudu