TSAN: avoid new link failure with -pg

Summary:
* Makefile (COMPILE_WITH_TSAN): Avoid a link failure by disabling
-pg when building with TSAN enabled.
Now that "make check" builds all $(PROGRAMS), it is linking
a few programs that were not normally linked before.
For example, this would fail to link with the following diagnostic:

  COMPILE_WITH_TSAN=1 make -j40 log_and_apply_bench

    CCLD     log_and_apply_bench
  ld: /usr/lib/../lib64/gcrt1.o: relocation R_X86_64_32S against `__libc_csu_fini' can not be used when making a shared object; recompile with -fPIC
  /usr/lib/../lib64/gcrt1.o: error adding symbols: Bad value
  collect2: error: ld returned 1 exit status
  Makefile:511: recipe for target 'log_and_apply_bench' failed
  make: *** [log_and_apply_bench] Error 1

Since removing -pg is sufficient to get past this link
failure, and no one cares about profiling TSAN-enabled
binaries anyway, we will refrain from linking with -pg
when TSAN testing is enabled.  Use a new variable, "pg"
which is set to "-pg" in most cases, but that is made
empty when COMPILE_WITH_TSAN is set.

Test Plan:
  Now, this succeeds:

    rm -f log_and_apply_bench
    COMPILE_WITH_TSAN=1 make -j40 log_and_apply_bench

Reviewers: igor.sugak, rven, sdong, ljin, igor

Reviewed By: igor

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D35943

Makefile

@@ -93,6 +93,11 @@ ifdef COMPILE_WITH_TSAN
 	EXEC_LDFLAGS += -fsanitize=thread -pie
 	PLATFORM_CCFLAGS += -fsanitize=thread -fPIC -DROCKSDB_TSAN_RUN
 	PLATFORM_CXXFLAGS += -fsanitize=thread -fPIC -DROCKSDB_TSAN_RUN
+        # Turn off -pg when enabling TSAN testing, because that induces
+        # a link failure.  TODO: find the root cause
+	pg =
+else
+	pg = -pg
 endif
 
 ifndef DISABLE_JEMALLOC
@@ -496,7 +501,7 @@ db_iter_test: db/db_iter_test.o $(LIBOBJECTS) $(TESTHARNESS)
 	$(AM_LINK)
 
 log_write_bench: util/log_write_bench.o $(LIBOBJECTS) $(TESTHARNESS)
-	$(AM_LINK) -pg
+	$(AM_LINK) $(pg)
 
 plain_table_db_test: db/plain_table_db_test.o $(LIBOBJECTS) $(TESTHARNESS)
 	$(AM_LINK)
@@ -505,10 +510,10 @@ comparator_db_test: db/comparator_db_test.o $(LIBOBJECTS) $(TESTHARNESS)
 	$(AM_LINK)
 
 table_reader_bench: table/table_reader_bench.o $(LIBOBJECTS) $(TESTHARNESS)
-	$(AM_LINK) -pg
+	$(AM_LINK) $(pg)
 
 log_and_apply_bench: db/log_and_apply_bench.o $(LIBOBJECTS) $(TESTHARNESS) $(BENCHHARNESS)
-	$(AM_LINK) -pg
+	$(AM_LINK) $(pg)
 
 perf_context_test: db/perf_context_test.o $(LIBOBJECTS) $(TESTHARNESS)
 	$(AM_V_CCLD)$(CXX) $^ $(EXEC_LDFLAGS) -o $@ $(LDFLAGS)