Remove tautological comparison.

Also build with -Wtype-limits to catch future instances.

Bug: 529
Change-Id: I2d84dc1824ffc7cd92411f49c9f953bcd3c74331
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/55045
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
Auto-Submit: David Benjamin <davidben@google.com>

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 69169c4..780ed21 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -132,7 +132,7 @@
 if(CMAKE_COMPILER_IS_GNUCXX OR CLANG)
   # Note clang-cl is odd and sets both CLANG and MSVC. We base our configuration
   # primarily on our normal Clang one.
-  set(C_CXX_FLAGS "-Werror -Wformat=2 -Wsign-compare -Wmissing-field-initializers -Wwrite-strings -Wvla -Wshadow")
+  set(C_CXX_FLAGS "-Werror -Wformat=2 -Wsign-compare -Wmissing-field-initializers -Wwrite-strings -Wvla -Wshadow -Wtype-limits")
   if(MSVC)
     # clang-cl sets different default warnings than clang. It also treats -Wall
     # as -Weverything, to match MSVC. Instead -W3 is the alias for -Wall.