Disable -Wthread-safety.

See changes file; closes ticket 20110.

changes/bug20110

@@ -0,0 +1,6 @@
+  o Minor bugfixes (compilation):
+
+    - Stop trying to build with Clang 4.0's -Wthread-safety
+      warnings. They apparently require a set of annotations that we
+      aren't currently using, and they create false positives in our
+      pthreads wrappers. Fixes bug 20110; bugfix on 0.2.9.1-alpha.

configure.ac

@@ -1800,11 +1800,6 @@ if test "x$enable_gcc_warnings_advisory" != "xno"; then
      -Wsync-nand
      -Wtautological-constant-out-of-range-compare
      -Wtentative-definition-incomplete-type
-     -Wthread-safety
-     -Wthread-safety-analysis
-     -Wthread-safety-attributes
-     -Wthread-safety-beta
-     -Wthread-safety-precise
      -Wtrampolines
      -Wtype-safety
      -Wtypedef-redefinition
@@ -1838,6 +1833,14 @@ if test "x$enable_gcc_warnings_advisory" != "xno"; then
      -Wzero-length-array
   ], [ TOR_CHECK_CFLAGS([warning_flag]) ])
 
+dnl    These seem to require annotations that we don't currently use,
+dnl    and they give false positives in our pthreads wrappers. (Clang 4)
+dnl     -Wthread-safety
+dnl     -Wthread-safety-analysis
+dnl     -Wthread-safety-attributes
+dnl     -Wthread-safety-beta
+dnl     -Wthread-safety-precise
+
   CFLAGS="$CFLAGS -W -Wfloat-equal -Wundef -Wpointer-arith"
   CFLAGS="$CFLAGS -Wstrict-prototypes -Wmissing-prototypes -Wwrite-strings"
   CFLAGS="$CFLAGS -Wredundant-decls -Wchar-subscripts -Wcomment -Wformat=2"