[clang-repl] Fix BUILD_SHARED_LIBS symbols from libclangInterpreter on MinGW (#71393)

A few symbols within libclangInterpreter have got explicit dllexport
attributes, in order to make them exported (and thus visible at runtime)
in any build, not only when they are part of e.g. a DLL libclang-cpp,
but also when they are part of a plain .exe.

Due to the explicit dllexports, these symbols would sidestep the regular
MinGW logic of exporting all symbols if there are no dllexports.
Therefore, for libclang-cpp, a separate fix was made in
592e935e, to pass --export-all-symbols
to the build of libclang-cpp.

If building with BUILD_SHARED_LIBS enabled, then the same issue appears
in libclangInterpreter; pass the same flag --export-all-symbols there as
well, to make sure all symbols are visible, not only the ones that are
explicitly marked as dllexport.