Use whichever mount gives the longest result. This change
is because argv[0] of MSYS2 programs was /bin/foo.exe when
it should be /usr/bin/foo.exe and this caused all sorts of
issues with relocation (as e.g. PREFIX is /usr and that is
expected to be found as the prefix of argv[0]).
For example, from cmd.exe:
"C:\msys64\usr\bin\g++.exe -print-prog-name=cc1plus"
.. gave:
"cc1plus"
.. before this patch, when it should have given:
"/usr/lib/gcc/x86_64-pc-msys/4.8.2/cc1plus.exe"
.. so that custom commandlines can be passed to
the debugger program using '|' as an argument
delimiter and <program-name> and <process-id>
as special tokens.
