[libcxx] Portability fix: close an open file stream before removing the file.

[amakc11]

Summary

The C standard says the following in the specification of the remove function: "If the file is open, the behavior of the remove function is implementation-defined". The recently added test fopens a file, but does not close it before calling the std::remove function on this file, thus making this test dependent on the type of filesystem used for running the test suite. This patch adds the missing std::fclose call. BTW, it's a good practice of clean programming.

[mclow.lists]

This looks fine to me.

[ldionne]

BTW, it's a good practice of clean programming.

Indeed, this was just a mistake on my part. Thanks for fixing.

test/std/input.output/stream.buffers/streambuf/streambuf.virtuals/streambuf.virt.put/xsputn.PR14074.pass.cpp

 // Count the number of bytes in a file -- make sure to use only functionality
 // provided by the C library to avoid relying on the C++ library, which we're
 // trying to test.
 static std::size_t count_bytes(char const* filename) {
     std::FILE* f = std::fopen(filename, "rb");
     std::size_t count = 0;
     while (std::fgetc(f) != EOF)
         ++count;
+    std::fclose(f);
     return count;
 }
 
 int main(int, char**) {
     {
         // with basic_stringbuf
         std::basic_stringbuf<char> buf;
         std::streamsize sz = buf.sputn("\xFF", 1);