Win32: Fix build on older versions of Visual C++

Older versions did not provide fmin or fmax.  This adds internal
versions of fminf and fmaxf that should not be confused with
standards compliant implementations.

src/init.c

@@ -119,6 +119,30 @@ char* _glfw_strdup(const char* source)
     return result;
 }
 
+float _glfw_fminf(float a, float b)
+{
+    if (a != a)
+        return b;
+    else if (b != b)
+        return a;
+    else if (a < b)
+        return a;
+    else
+        return b;
+}
+
+float _glfw_fmaxf(float a, float b)
+{
+    if (a != a)
+        return b;
+    else if (b != b)
+        return a;
+    else if (a > b)
+        return a;
+    else
+        return b;
+}
+
 
 //////////////////////////////////////////////////////////////////////////
 //////                         GLFW event API                       //////

src/input.c

@@ -1242,7 +1242,7 @@ GLFWAPI int glfwGetGamepadState(int jid, GLFWgamepadstate* state)
         if (e->type == _GLFW_JOYSTICK_AXIS)
         {
             const float value = js->axes[e->index] * e->axisScale + e->axisOffset;
-            state->axes[i] = fminf(fmaxf(value, -1.f), 1.f);
+            state->axes[i] = _glfw_fminf(_glfw_fmaxf(value, -1.f), 1.f);
         }
         else if (e->type == _GLFW_JOYSTICK_HATBIT)
         {

src/internal.h

@@ -766,4 +766,6 @@ void _glfwTerminateVulkan(void);
 const char* _glfwGetVulkanResultString(VkResult result);
 
 char* _glfw_strdup(const char* source);
+float _glfw_fminf(float a, float b);
+float _glfw_fmaxf(float a, float b);