Allow multi-word "install" command.

Autoconf can determine that the correct install command includes flags,
e.g., "/usr/bin/install -c". When using this as a command, we can't
enclose the value in double-quotes, as that makes some shells use the
whole expression as a filename:

# this is the value returned by autoconf and stored in CT_install
$ ins="/usr/bin/install -c"

# if we call it with quotes, the command is not found
$ "${ins}"
bash: /usr/bin/install -c: No such file or directory

# removing the quotes lets it work as expected
$ ${ins}
/usr/bin/install: missing file operand
Try `/usr/bin/install --help' for more information.

Signed-Off-By: Anthony Foiani <anthony.foiani@gmail.com>

 # mingw options

 ## depends on MINGW32

 ##

 ## select LIBC_SUPPORT_WIN32THREADS

 ##

 ## help The de-facto standard for Mingw distributions.

 choice

     bool

     prompt "Mingw runtime version"

 # Don't remove next line

 # CT_INSERT_VERSION_BELOW

 config MINGWRT_V_3_18

     bool

     prompt "3.18"

 config MINGWRT_V_select

     bool

     prompt "Other version"

 endchoice

 config MINGWRT_VERSION

     string

     prompt "Mingw runtime version" if MINGWRT_V_select

 # Don't remove next line

 # CT_INSERT_VERSION_STRING_BELOW

     default "3.18" if MINGWRT_V_3_18

     help

       Enter the version number of the mingw runtime files to use