Fix conflict with DEBUG macro defined by Bazel

The Bazel build system may define DEBUG when compiling on macOS, which
caused the glfwinfo test program to fail to build.

Fixes glfw#1537.

Author: elmindreda

tests/glfwinfo.c

@@ -318,7 +318,8 @@ int main(int argc, char** argv)
     int ch;
     bool list_extensions = false, list_layers = false;
 
-    enum { CLIENT, CONTEXT, BEHAVIOR, DEBUG, FORWARD, HELP, EXTENSIONS, LAYERS,
+    enum { CLIENT, CONTEXT, BEHAVIOR, DEBUG_CONTEXT, FORWARD, HELP,
+           EXTENSIONS, LAYERS,
            MAJOR, MINOR, PROFILE, ROBUSTNESS, VERSION,
            REDBITS, GREENBITS, BLUEBITS, ALPHABITS, DEPTHBITS, STENCILBITS,
            ACCUMREDBITS, ACCUMGREENBITS, ACCUMBLUEBITS, ACCUMALPHABITS,
@@ -329,7 +330,7 @@ int main(int argc, char** argv)
         { "behavior",           1, NULL, BEHAVIOR },
         { "client-api",         1, NULL, CLIENT },
         { "context-api",        1, NULL, CONTEXT },
-        { "debug",              0, NULL, DEBUG },
+        { "debug",              0, NULL, DEBUG_CONTEXT },
         { "forward",            0, NULL, FORWARD },
         { "help",               0, NULL, HELP },
         { "list-extensions",    0, NULL, EXTENSIONS },
@@ -420,7 +421,7 @@ int main(int argc, char** argv)
                 }
                 break;
             case 'd':
-            case DEBUG:
+            case DEBUG_CONTEXT:
                 glfwWindowHint(GLFW_OPENGL_DEBUG_CONTEXT, GLFW_TRUE);
                 break;
             case 'f':