Workaround missing std::nextafter in uClibc

Luckily, the rest of C++11 features seem to be supported...

Closes #1739

include/internal/catch_compiler_capabilities.h

@@ -197,6 +197,10 @@
     #define CATCH_CONFIG_COLOUR_NONE
 #endif
 
+#if defined(__UCLIBC__)
+#define CATCH_INTERNAL_CONFIG_GLOBAL_NEXTAFTER
+#endif
+
 ////////////////////////////////////////////////////////////////////////////////
 // Check if string_view is available and usable
 // The check is split apart to work around v140 (VS2015) preprocessor issue...
@@ -306,6 +310,10 @@
 #  define CATCH_CONFIG_ANDROID_LOGWRITE
 #endif
 
+#if defined(CATCH_INTERNAL_CONFIG_GLOBAL_NEXTAFTER) && !defined(CATCH_CONFIG_NO_GLOBAL_NEXTAFTER) && !defined(CATCH_CONFIG_GLOBAL_NEXTAFTER)
+#  define CATCH_CONFIG_GLOBAL_NEXTAFTER
+#endif
+
 #if !defined(CATCH_INTERNAL_SUPPRESS_PARENTHESES_WARNINGS)
 #   define CATCH_INTERNAL_SUPPRESS_PARENTHESES_WARNINGS
 #   define CATCH_INTERNAL_UNSUPPRESS_PARENTHESES_WARNINGS

include/internal/catch_matchers_floating.cpp

@@ -11,13 +11,16 @@
 #include "catch_to_string.hpp"
 #include "catch_tostring.h"
 
+#include <cmath>
 #include <cstdlib>
 #include <cstdint>
 #include <cstring>
 #include <sstream>
+#include <type_traits>
 #include <iomanip>
 #include <limits>
 
+
 namespace Catch {
 namespace Matchers {
 namespace Floating {
@@ -77,10 +80,32 @@ bool almostEqualUlps(FP lhs, FP rhs, int maxUlpDiff) {
     return ulpDiff <= maxUlpDiff;
 }
 
+#if defined(CATCH_CONFIG_GLOBAL_NEXTAFTER)
+
+namespace Catch {
+    float nextafter(float x, float y) {
+        return ::nextafterf(x, y);
+    }
+
+    double nextafter(double x, double y) {
+        return ::nextafter(x, y);
+    }
+
+    long double nextafter(long double x, long double y) {
+        return ::nextafterl(x, y);
+    }
+} // end namespace Catch
+
+#endif
+
 template <typename FP>
 FP step(FP start, FP direction, int steps) {
     for (int i = 0; i < steps; ++i) {
+#if defined(CATCH_CONFIG_GLOBAL_NEXTAFTER)
+        start = Catch::nextafter(start, direction);
+#else
         start = std::nextafter(start, direction);
+#endif
     }
     return start;
 }

include/internal/catch_matchers_floating.h

@@ -9,9 +9,6 @@
 
 #include "catch_matchers.h"
 
-#include <type_traits>
-#include <cmath>
-
 namespace Catch {
 namespace Matchers {