Confusing error message when mod.export_library() with non-standard library suffix

When dump compiled library with lib.export_library(filename), if the filename does not end with “.so” or “.dylib”, there will lead to compiler error like

Traceback (most recent call last):
  File "", line 14, in <module>
  File "/incubator-tvm/python/tvm/runtime/", line 340, in export_library
    fcompile(file_name, files, **kwargs)
  File "/incubator-tvm/python/tvm/contrib/", line 48, in create_shared
    _linux_compile(output, objects, options, cc)
  File "/incubator-tvm/python/tvm/contrib/", line 189, in _linux_compile
    raise RuntimeError(msg)
RuntimeError: Compilation error:
/lib/../lib64/crt1.o:In function `_start':
(.text+0x20):undefined reference to 'main'
collect2: error: ld returned 1 exit status

Since we almost always expect to export shared library (except tar), can this restrict be removed or more friendly noted? The current error is somewhat confusing.

One quick fix PR is here: