Fixes for MinGW compatibility

Some versions of MinGW do not support enough of Win32 API to let us work
with SEH, so SEH is now MSVC only (+ configurable toggle).

Also made use of gmtime_s MSVC only (as oposed to Windows only).

Fixes #805

docs/configuration.md

@@ -1,6 +1,6 @@
 Catch is designed to "just work" as much as possible. For most people the only configuration needed is telling Catch which source file should host all the implementation code (```CATCH_CONFIG_MAIN```).
 
-Nonetheless there are still some occasions where finer control is needed. For these occasions Catch exposes a small set of macros for configuring how it is built.
+Nonetheless there are still some occasions where finer control is needed. For these occasions Catch exposes a set of macros for configuring how it is built.
 
 #  main()/ implementation
 
@@ -70,6 +70,15 @@ You may also suppress any of these features by using the `_NO_` form, e.g. `CATC
 
 All C++11 support can be disabled with `CATCH_CONFIG_NO_CPP11`
 
+# Other toggles
+
+    CATCH_CONFIG_COUNTER                    // Use __COUNTER__ to generate unique names for test cases
+    CATCH_CONFIG_WINDOWS_SEH                // Enable SEH handling on Windows
+
+Currently Catch enables `CATCH_CONFIG_WINDOWS_SEH` only when compiled with MSVC, because some versions of MinGW do not have the necessary Win32 API supports.
+
+Just as with the C++11 conformance toggles, these toggles can be disabled by using `_NO_` form of the toggle, e.g. `CATCH_CONFIG_NO_WINDOWS_SEH`.
+
 # Windows header clutter
 
 On Windows Catch includes `windows.h`. To minimize global namespace clutter in the implementation file, it defines `NOMINMAX` and `WIN32_LEAN_AND_MEAN` before including it. You can control this behaviour via two macros:

include/internal/catch_compiler_capabilities.h

@@ -26,6 +26,7 @@
 
 // CATCH_CONFIG_VARIADIC_MACROS : are variadic macros supported?
 // CATCH_CONFIG_COUNTER : is the __COUNTER__ macro supported?
+// CATCH_CONFIG_WINDOWS_SEH : is Windows SEH supported?
 // ****************
 // Note to maintainers: if new toggles are added please document them
 // in configuration.md, too
@@ -109,6 +110,8 @@
 // Visual C++
 #ifdef _MSC_VER
 
+#define CATCH_INTERNAL_CONFIG_WINDOWS_SEH
+
 #if (_MSC_VER >= 1600)
 #   define CATCH_INTERNAL_CONFIG_CPP11_NULLPTR
 #   define CATCH_INTERNAL_CONFIG_CPP11_UNIQUE_PTR
@@ -233,6 +236,9 @@
 # if defined(CATCH_INTERNAL_CONFIG_CPP11_TYPE_TRAITS) && !defined(CATCH_CONFIG_CPP11_NO_TYPE_TRAITS) && !defined(CATCH_CONFIG_CPP11_TYPE_TRAITS) && !defined(CATCH_CONFIG_NO_CPP11)
 #  define CATCH_CONFIG_CPP11_TYPE_TRAITS
 # endif
+#if defined(CATCH_INTERNAL_CONFIG_WINDOWS_SEH) && !defined(CATCH_CONFIG_NO_WINDOWS_SEH) && !defined(CATCH_CONFIG_WINDOWS_SEH)
+#   define CATCH_CONFIG_WINDOWS_SEH
+#endif
 
 #if !defined(CATCH_INTERNAL_SUPPRESS_PARENTHESES_WARNINGS)
 #   define CATCH_INTERNAL_SUPPRESS_PARENTHESES_WARNINGS

include/internal/catch_fatal_condition.hpp

@@ -22,10 +22,17 @@ namespace Catch {
 } // namespace Catch
 
 #if defined ( CATCH_PLATFORM_WINDOWS ) /////////////////////////////////////////
-
-
 #include "catch_windows_h_proxy.h"
 
+#  if !defined ( CATCH_CONFIG_WINDOWS_SEH )
+
+namespace Catch {
+    struct FatalConditionHandler {
+        void reset() {}        
+    };
+}
+
+#  else // CATCH_CONFIG_WINDOWS_SEH is defined
 
 namespace Catch {
 
@@ -84,6 +91,8 @@ namespace Catch {
 
 } // namespace Catch
 
+#  endif // CATCH_CONFIG_WINDOWS_SEH
+
 #else // Not Windows - assumed to be POSIX compatible //////////////////////////
 
 #include <signal.h>

include/reporters/catch_reporter_junit.hpp

@@ -26,7 +26,7 @@ namespace Catch {
             std::time(&rawtime);
             const size_t timeStampSize = sizeof("2017-01-16T17:06:45Z");
 
-#ifdef CATCH_PLATFORM_WINDOWS
+#ifdef _MSC_VER
             std::tm timeInfo = {};
             gmtime_s(&timeInfo, &rawtime);
 #else
@@ -37,7 +37,7 @@ namespace Catch {
             char timeStamp[timeStampSize];
             const char * const fmt = "%Y-%m-%dT%H:%M:%SZ";
 
-#ifdef CATCH_PLATFORM_WINDOWS
+#ifdef _MSC_VER
             std::strftime(timeStamp, timeStampSize, fmt, &timeInfo);
 #else
             std::strftime(timeStamp, timeStampSize, fmt, timeInfo);