MSYS/MinGW support

Apparently there is considerable interest in supporting builds within MSYS/MinGW for Windows rather than cygwin or cross compiling MinGW from (e.g.) Linux.

The main difficulty in supporting this platform is that MinGW doesn’t support fork/exec (or actually vfork/exec) and thus exec support in the bootstrap jimsh is limited.

Fortunately, autosetup has few requirements of exec and these limitations can be worked around, along with other differences such as the use of backlashes in paths.

autosetup running under the MSYS bash shell

$ cd examples/typical
$ ./configure
No installed jimsh or tclsh, building local bootstrap jimsh0
Host System...i686-pc-mingw32
Build System...i686-pc-mingw32
C compiler... gcc -g -O2
C++ compiler... c++ -g -O2
Checking for stdlib.h...ok
Checking for long long...ok
Checking for sizeof long long...8
Checking for sizeof void *...4
Checking for sys/un.h...not found
Checking for regcomp...not found
Checking for waitpid...not found
Checking for sigaction...not found
Checking for sys_signame...not found
Checking for sys_siglist...not found
Checking for syslog...not found
Checking for opendir...ok
Checking for readlink...not found
Checking for sleep...not found
Checking for usleep...ok
Checking for pipe...not found
Checking for inet_ntop...not found
Checking for getaddrinfo...not found
Enabling UTF-8
Building static library
Created config.h
Created Makefile from Makefile.in