Fix typos identified using codespell

See https://github.com/codespell-project/codespell#readme

The following command was used:

```
codespell -q6 --skip="\
.git,\
*.json,\
./Copyright.txt,\
./Help/command/foreach.rst,\
./Help/prop_test/REQUIRED_FILES.rst,\
./Help/variable/CTEST_COVERAGE_COMMAND.rst,\
./Modules/CMakeCheckCompilerFlagCommonPatterns.cmake,\
./Modules/CMakeRCInformation.cmake,\
./Modules/Internal/CPack/NSIS.template.in,\
./Modules/FindMatlab.cmake,\
./Modules/MatlabTestsRedirect.cmake,\
./Modules/Platform/Windows-Clang.cmake,\
./Modules/Platform/Windows-Intel-Fortran.cmake,\
./Modules/Platform/Windows-MSVC.cmake,\
./Source/CMakeVersion.cmake,\
./Source/cmConvertMSBuildXMLToJSON.py,\
./Source/cmCreateTestSourceList.cxx,\
./Source/cmGlobalVisualStudio10Generator.cxx,\
./Source/cmExportBuildFileGenerator.cxx,\
./Source/cmExportInstallAndroidMKGenerator.cxx,\
./Source/cmExportInstallFileGenerator.cxx,\
./Source/cmExportSet.cxx,\
./Source/cmExportTryCompileFileGenerator.cxx,\
./Source/cmFindPackageCommand.cxx,\
./Source/cmInstallCommand.cxx,\
./Source/cmGeneratorExpressionLexer.cxx,\
./Source/cmLocalVisualStudio7Generator.cxx,\
./Source/cmOrderDirectories.cxx,\
./Source/cmTarget.cxx,\
./Source/kwsys/*,\
./Source/QtDialog/CMakeSetupDialog.ui,\
./Source/CPack/WiX/cmWIXRichTextFormatWriter.cxx,\
./Source/CTest/cmParseCoberturaCoverage.h,\
./Tests/CMakeTests/ImplicitLinkInfoTest.cmake.in,\
./Tests/RunCMake/CPack/tests/DMG_SLA/English.license.rtf,\
./Tests/RunCMake/CPack/tests/DMG_SLA/German.license.txt,\
./Tests/RunCMake/CPack/tests/DMG_SLA/German.menu.txt,\
./Tests/RunCMake/GoogleTest/xml_output.cpp,\
./Tests/RunCMake/Make/TargetMessages*,\
./Utilities/*,\
" \
-L "\
dependees,\
endwhile,\
fo,\
filetest,\
helpfull,\
nd,\
objext,\
stoll,\
supercedes,\
superceded,\
vas,\
varn,\
"
```

Modules/Compiler/ARMClang.cmake

@@ -98,7 +98,7 @@ macro(__compiler_armclang lang)
       set(__mcpu_flag_set TRUE)
     endif()
     if(NOT __march_flag_set AND NOT __mcpu_flag_set)
-      message(FATAL_ERROR "Atleast one of the variables CMAKE_SYSTEM_PROCESSOR or CMAKE_SYSTEM_ARCH must be set for ARMClang\n"
+      message(FATAL_ERROR "At least one of the variables CMAKE_SYSTEM_PROCESSOR or CMAKE_SYSTEM_ARCH must be set for ARMClang\n"
                           "Supported processor: ${CMAKE_${lang}_COMPILER_PROCESSOR_LIST}\n"
                           "  Supported Architecture: ${CMAKE_${lang}_COMPILER_ARCH_LIST}")
     endif()

Modules/Compiler/OpenWatcom.cmake

@@ -86,7 +86,7 @@ set(CMAKE_C_CREATE_STATIC_LIBRARY
 set(CMAKE_CXX_CREATE_STATIC_LIBRARY ${CMAKE_C_CREATE_STATIC_LIBRARY})
 
 
-# old CMake internaly used OpenWatcom version macros
+# old CMake internally used OpenWatcom version macros
 # for backward compatibility
 if(NOT _CMAKE_WATCOM_VERSION)
   set(_CMAKE_WATCOM_VERSION 1)