Add more xcode configurations to Travis

Travis CI shows linking errors on Linux and OS X when __cxa_uncaught_exceptions
is used to implement uncaught_exceptions. There's probably some library missing,
which should be linked in implicitly by the compiler, or the library indeed
does not export the symbol. In any case, __cxa_get_globals-based implementation
should provide the same effect.

.travis.yml

@@ -240,6 +240,7 @@ matrix:
         apt:
           packages:
             - libc++-dev
+            - libc++abi-dev
 
     - os: linux
       compiler: clang++-libc++
@@ -248,10 +249,27 @@ matrix:
         apt:
           packages:
             - libc++-dev
+            - libc++abi-dev
 
     - os: osx
       compiler: clang++
       env: TOOLSET=clang COMPILER=clang++ CXXSTD=03,11,14,1z
+      osx_image: xcode7.3
+
+    - os: osx
+      compiler: clang++
+      env: TOOLSET=clang COMPILER=clang++ CXXSTD=03,11,14,1z
+      osx_image: xcode8.3
+
+    - os: osx
+      compiler: clang++
+      env: TOOLSET=clang COMPILER=clang++ CXXSTD=03,11,14,1z
+      osx_image: xcode9.4
+
+    - os: osx
+      compiler: clang++
+      env: TOOLSET=clang COMPILER=clang++ CXXSTD=03,11,14,1z
+      osx_image: xcode10.1
 
     - os: linux
       compiler: g++

include/boost/core/uncaught_exceptions.hpp

@@ -46,20 +46,36 @@
 #if defined(BOOST_CORE_HAS_CXXABI_H)
 // MinGW GCC 4.4 seem to not work the same way the newer GCC versions do. As a result, __cxa_get_globals based implementation will always return 0.
 // Just disable it for now and fall back to std::uncaught_exception().
-#if !defined(__MINGW32__) || (defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 5)))
-#define BOOST_CORE_HAS_CXA_GET_GLOBALS
+#if !(defined(__MINGW32__) && (defined(__GNUC__) && (__GNUC__ * 100 + __GNUC_MINOR__) < 405))
 #include <cxxabi.h>
-// Only GCC 4.7 declares __cxa_get_globals() in cxxabi.h, older compilers do not expose this function but it's there
-#if defined(__GNUC__) && (__GNUC__ * 100 + __GNUC_MINOR__) < 407
+#include <cstring>
+#define BOOST_CORE_HAS_CXA_GET_GLOBALS
+// At least on MinGW and Linux, only GCC since 4.7 declares __cxa_get_globals() in cxxabi.h. Older versions of GCC do not expose this function but it's there.
+// On OpenBSD, it seems, the declaration is also missing.
+// Note that at least on FreeBSD 11, cxxabi.h declares __cxa_get_globals with a different exception specification, so we can't declare the function unconditionally.
+// On Linux with clang and libc++ and on OS X, there is a version of cxxabi.h from libc++abi that doesn't declare __cxa_get_globals, but provides __cxa_uncaught_exceptions.
+// The function only appeared in version _LIBCPPABI_VERSION >= 1002 of the library. Unfortunately, there are linking errors about undefined reference to __cxa_uncaught_exceptions
+// on Ubuntu Trusty and OS X, so we avoid using it and forward-declare __cxa_get_globals instead.
+#if !defined(__FreeBSD__) && \
+    ( \
+        (defined(__GNUC__) && (__GNUC__ * 100 + __GNUC_MINOR__) < 407) || \
+        defined(__OpenBSD__) || \
+        defined(_LIBCPPABI_VERSION) \
+    )
 namespace __cxxabiv1 {
 struct __cxa_eh_globals;
+#if defined(__OpenBSD__)
+extern "C" __cxa_eh_globals* __cxa_get_globals();
+#else
 extern "C" __cxa_eh_globals* __cxa_get_globals() BOOST_NOEXCEPT_OR_NOTHROW __attribute__((__const__));
-} // namespace __cxxabiv1
-#endif // defined(__GNUC__) && (__GNUC__ * 100 + __GNUC_MINOR__) < 407
 #endif
+} // namespace __cxxabiv1
+#endif
+#endif // !(defined(__MINGW32__) && (defined(__GNUC__) && (__GNUC__ * 100 + __GNUC_MINOR__) < 405))
 #endif // defined(BOOST_CORE_HAS_CXXABI_H)
 
 #if defined(_MSC_VER) && _MSC_VER >= 1400
+#include <cstring>
 #define BOOST_CORE_HAS_GETPTD
 namespace boost {
 namespace core {
@@ -89,10 +105,14 @@ inline unsigned int uncaught_exceptions() BOOST_NOEXCEPT
     return static_cast< unsigned int >(std::uncaught_exceptions());
 #elif defined(BOOST_CORE_HAS_CXA_GET_GLOBALS)
     // Tested on {clang 3.2,GCC 3.5.6,GCC 4.1.2,GCC 4.4.6,GCC 4.4.7}x{x32,x64}
-    return *(reinterpret_cast< const unsigned int* >(reinterpret_cast< const char* >(::abi::__cxa_get_globals()) + sizeof(void*))); // __cxa_eh_globals::uncaughtExceptions, x32 offset - 0x4, x64 - 0x8
+    unsigned int count;
+    std::memcpy(&count, reinterpret_cast< const unsigned char* >(::abi::__cxa_get_globals()) + sizeof(void*), sizeof(count)); // __cxa_eh_globals::uncaughtExceptions, x32 offset - 0x4, x64 - 0x8
+    return count;
 #elif defined(BOOST_CORE_HAS_GETPTD)
     // MSVC specific. Tested on {MSVC2005SP1,MSVC2008SP1,MSVC2010SP1,MSVC2012}x{x32,x64}.
-    return *(reinterpret_cast< const unsigned int* >(static_cast< const char* >(boost::core::detail::_getptd()) + (sizeof(void*) == 8 ? 0x100 : 0x90))); // _tiddata::_ProcessingThrow, x32 offset - 0x90, x64 - 0x100
+    unsigned int count;
+    std::memcpy(&count, static_cast< const unsigned char* >(boost::core::detail::_getptd()) + (sizeof(void*) == 8u ? 0x100 : 0x90), sizeof(count)); // _tiddata::_ProcessingThrow, x32 offset - 0x90, x64 - 0x100
+    return count;
 #else
     // Portable C++03 implementation. Does not allow to detect multiple nested exceptions.
     return static_cast< unsigned int >(std::uncaught_exception());