Build with -fno-exceptions standalone.

This serves two purposes:

1. Make sure we don't accidentally write "throw" or "catch" in our code.

2. If a C project statically links to our libssl.a, they'll use gcc
   rather than g++ as the linker which does not pull in the C++ runtime.
   -fno-exceptions cuts out the C++ runtime dependency. (Though we will
   need to give up on this should we attempt to allow a runtime
   dependency in the future.)

Bug: 132
Change-Id: I9fc81f034833ec9ed38b98d98df7b45c32cfa30c
Reviewed-on: https://boringssl-review.googlesource.com/18084
Reviewed-by: Steven Valdez <svaldez@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index cddffe2..3c2d556 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -42,7 +42,7 @@
     set(C_CXX_FLAGS "${C_CXX_FLAGS} -Wno-free-nonheap-object")
   endif()
   set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${C_CXX_FLAGS} -Wmissing-prototypes -Wold-style-definition -Wstrict-prototypes")
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 ${C_CXX_FLAGS} -Wmissing-declarations")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 ${C_CXX_FLAGS} -Wmissing-declarations -fno-exceptions")
   # In GCC, -Wmissing-declarations is the C++ spelling of -Wmissing-prototypes
   # and using the wrong one is an error. In Clang, -Wmissing-prototypes is the
   # spelling for both and -Wmissing-declarations is some other warning.