clearer readme

README.md

@@ -18,17 +18,42 @@ files in there directly if you don't need the API documentation.
 ## Building
 
 Libostd is built using the supplied C++ build tool. You need to compile the
-build tool first using the compiler you will use to build the library itself:
+build tool first using the compiler you will use to build the library itself.
+
+On a typical setup, this will involve:
 
 ~~~
-c++ build.cc -o build -std=c++1z
+c++ build.cc -o build -std=c++1z -I. -pthread
+./build --help
 ~~~
 
-On Unix-like systems, the `-pthread` option is necessary. C++17 is required
+This will typically build using either GCC or Clang with typically libstdc++
-to build it just like the library itself. If you're using libc++ and your
+as a standard library implementation. **Keep in mind that it is you need
-version does not supply a stable `std::filesystem` module, you will also
+at least Clang 4.0 or GCC 7.1 to build.** To switch to libc++:
-need to link `-lc++experimental`. If you have the same issue with libstdc++,
+
-the necessary linker flag is `-lstdc++fs`.
+~~~
+c++ build.cc -o build -std=c++1z -I. -pthread -stdlib=libc++
+CXXFLAGS="-stdlib=libc++" ./build
+~~~
+
+If you get undefined references about filesystem, you will need to add
+extra linkage.
+
+For libstdc++:
+
+~~~
+c++ build.cc -o build -std=c++1z -I. -pthread -lstdc++fs
+LDFLAGS="-lstdc++fs" ./build
+~~~
+
+For libc++:
+
+~~~
+c++ build.cc -o build -std=c++1z -I. -pthread -stdlib=libc++ -lc++experimental
+CXXFLAGS="-stdlib=libc++" LDFLAGS="-lc++experimental" ./build
+~~~
+
+You can skip `-pthread` on Windows.
 
 Using the tool should be straightforward. The `./build --help` command lists
 the available options.