cc58ca5370
-isysroot flag was added to all tests, but it makes Driver/darwin-version.f90 failed. In fact, only a few tests regarding interoperability with C need -isysroot flag to search for headers and libraries. So, -isysroot flag is now eliminated from the substitution `%flang`, and a new substitution `%isysroot` has been introduced. Moreover, Integration/iso-fortran-binding.cpp invokes clang++ via a shell script, which makes it hard to add -isysroot flag. So, it is refactored. Fixes #150765
Flang Integration Tests
This directory can be used to add Integration tests involving multiple stages of the compiler (for eg. from Fortran to LLVM IR). It should not contain executable tests. We should only add tests here sparingly and only if there is no other way to test. Repeat this message in each test that is added to this directory and sub-directories.