Made flatc error messages look like what other compilers output.

Looks like MSVC on Windows and like gcc everywhere else.
For enhanced IDE clickability.

Bug: 17208371
Change-Id: Ie3e02658fccd3edfd464b4bacf4bc68c613a8570
Tested: on Linux and Windows.

include/flatbuffers/util.h

@@ -24,9 +24,18 @@
 #include <stdlib.h>
 #include <assert.h>
 #ifdef _WIN32
+#ifndef WIN32_LEAN_AND_MEAN
+  #define WIN32_LEAN_AND_MEAN
+#endif
+#ifndef NOMINMAX
+  #define NOMINMAX
+#endif
+#include <windows.h>
+#include <winbase.h>
 #include <direct.h>
 #else
 #include <sys/stat.h>
+#include <limits.h>
 #endif
 
 namespace flatbuffers {
@@ -157,6 +166,20 @@ inline void EnsureDirExists(const std::string &filepath) {
   #endif
 }
 
+// Obtains the absolute path from any other path.
+// Returns the input path if the absolute path couldn't be resolved.
+inline std::string AbsolutePath(const std::string &filepath) {
+  #ifdef _WIN32
+    char abs_path[MAX_PATH];
+    return GetFullPathNameA(filepath.c_str(), MAX_PATH, abs_path, nullptr)
+  #else
+    char abs_path[PATH_MAX];
+    return realpath(filepath.c_str(), abs_path)
+  #endif
+    ? abs_path
+    : filepath;
+}
+
 // To and from UTF-8 unicode conversion functions
 
 // Convert a unicode code point into a UTF-8 representation by appending it