Clang on Windows with MinGW

I have both MinGW gcc and Clang clang installed and added to path via chocolatey, and both can be found on the command line. However, when I try to use clang with gcc, clang doesn't seem to know where to find header files in the standard library (such as iostream), returning the following error:

clang++ -v main.cpp -o main.exe -std=c++14 -target x86_64-mingw64

clang version 9.0.0 (tags/RELEASE_900/final)
Target: x86_64-unknown-windows-gnu
Thread model: posix
InstalledDir: C:\Program Files\LLVM\bin
(SKIP)
ignoring nonexistent directory "(nonexistent directories)"
#include "..." search starts here:
#include <...> search starts here:
C:\Program Files\LLVM\lib\clang\9.0.0\include
End of search list.
main.cpp:1:10: fatal error: 'iostream' file not found
#include <iostream>
         ^~~~~~~~~~
1 error generated.

shell returned 1

I've added both gcc and clang to path, as well as the directory containing header files included in gcc (C:\ProgramData\chocolatey\lib\mingw\tools\install\mingw64\lib\gcc\x86_64-w64-mingw32\8.1.0), so I don't understand why clang isn't looking in the right place for the header files. How can I fix this problem? And this isn't really necessary, but can the default target for clang be changed? The current Windows 10 default for clang is msvc, but I'd rather not use it.