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Fixes: #18700

Fixes: #14983, #16561

Ancient CMake versions required upper-case commands.  Later command
names became case-insensitive.  Now the preferred style is lower-case.

Run the following shell code:

cmake --help-command-list |
grep -v "cmake version" |
while read c; do
    echo 's/\b'"$(echo $c | tr '[:lower:]' '[:upper:]')"'\(\s*\)(/'"$c"'\1(/g'
done >convert.sed &&
git ls-files -z -- bootstrap '*.cmake' '*.cmake.in' '*CMakeLists.txt' |
egrep -z -v '^(Utilities/cm|Source/kwsys/)' |
xargs -0 sed -i -f convert.sed &&
rm convert.sed

Store in new platform variables

  CMAKE_${lang}_COMPILE_OPTIONS_PIC
  CMAKE_${lang}_COMPILE_OPTIONS_PIE

flags for position independent code generation.

In almost all cases, this means duplication of the
CMAKE_SHARED_LIBRARY_${lang}_FLAGS for the _PIC case and using the
assumed pie equivalent for the _PIE case.  Note that the GNU compiler
has supported -fPIE since 3.4 and that there is no -fPIC on GNU for
Windows or Cygwin.

There is a possibility that the _PIE variables are not correct.
However, as there is no backwards compatibility to be concerned about
(as the POSITION_INDEPENDENT_CODE property is not used anywhere yet),
the current state suffices.

ENH: more uniform approach to enable language, one step closer to being able to enable a language without modifing cmake source code