MSYS is a Unix emulation environment for Windows, and is specifically designed such that in normal usage it pretends to be MinGW or native Windows, but understands Unix-style file names and paths, and supports standard Unix tools and shells. Thus, “native” MinGW builds are actually an odd sort of cross-compile, from an MSYS Unix emulation environment “pretending” to be MinGW, to actual native Windows.
When an MSYS shell launches a native Windows executable (as opposed to other
MSYS executables), it uses a system of heuristics to detect any
command-line arguments that contain file names or paths. It automatically
converts these file names from the MSYS (Unix-like) format, to the
corresponding Windows file name, before launching the executable. However,
this auto-conversion facility is only available when using the MSYS runtime
library. The wrapper executable itself is a MinGW application (that is, it
does not use the MSYS runtime library). The wrapper executable must set
PATH to, and call _spawnv with, values that have already been
converted from MSYS format to Windows. Thus, when libtool writes the source
code for the wrapper executable, it must manually convert MSYS paths to
Windows format, so that the Windows values can be hard-coded into the wrapper
executable.