Add cached variable WITH_XXX_STORAGE_ENGINE for dynamic plugins that can be static or 
dynamic.

This finishes of moving code from configure.cmake IF()'s to platform specific files

cmake/os/SunOS.cmake:
  WL#5161: Moved Solaris specific  workaround to cmake/os/SunOS.cmake

under cmake/os. This patch does it for Linux

WL#5161: Implement Mats' suggestion of moving OS specific CMake code to OS specific files, instead of 
polluting code with IF(CMAKE_SYSTEM_NAME MATCHES...), first on Windows.

cmake/libutils.cmake:
  Fix the case in MERGE_LIBRARIES, where  there is no dependency on OS libraries.
cmake/os/Windows.cmake:
  Move windows specific code to cmake/os/Windows.cmake
configure.cmake:
  Move some Windows code to cmake/os/Windows.cmake

- opensolaris cmake package is SUNWcmake not SUNWCMake
- it is configure.cmake not config.cmake

compile embedded with PIC to allow linking with shared libraries

Following autotools tradition, add preprocessor definitions  specified in environment variable CPPFLAGS

Fix failing sys_vars.plugin_dir_basic - treat both '/' and '\' as path separators in get_relative_path() on Windows

using  cmake option INSTALL_LAYOUT=STANDALONE would produce the layout as in 
tar.gz or zip packages.
INSTALL_LAYOUT=UNIX will produce unixish install layout  (with mysqld being in sbin subdirectory , libs in lib/mysql etc). This layout is used for RPM packages.

Subtle differences in both packages unfortunately lead to the need to recompile MySQL to use with other package type - as otherwise for example default plugins or data directories would be wrong set.

There are numerous other variables that  allow fine-tuning packaging layout. (INSTALL_BINDIR, INSTALL_LIBDIR , INSTALL_PLUGINDIR etc).

This options are different from autotools as they do not expect full paths to directories, but only subdirectory of CMAKE_INSTALL_PREFIX.

There are 2 special options that expect full directory paths
- MYSQL_DATADIR that defines default MYSQL data directory (autotools equivalent
is --localstatedir)
- SYSCONFDIR  can be added to search my.cnf search path (autotools equivalent is --sysconfdir)

 WORDS_BIGENDIAN was wrongly defined to 1

and later

in errmsg.txt. Kept the one in that matched the location
in errmsg-utf8.txt, ie after ER_UNKNOWN_LOCALE.