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>

 # Menu for the native GDB

 config GDB_NATIVE

     bool

     prompt "Native gdb"

     depends on ! BARE_METAL

     depends on ! BACKEND

     help

       Build and install a native gdb for the target, to run on the target.

 if GDB_NATIVE

 config GDB_NATIVE_STATIC

     bool

     prompt "Build a static native gdb"

     help

       In case you have trouble with dynamic loading of shared libraries,

       you will find that a static gdb comes in handy.

 endif # GDB_NATIVE