cmTarget: Refactor GetLocation API

When given a non-NULL configuration the GetLocation returned the
location for the given configuration.  When given a NULL configuration
the GetLocation method returned a location with the build-system
placeholder for the configuration name.  Split the latter use case out
into a separate GetLocationForBuild method and update call sites
accordingly.
stringapi: Pass configuration names as strings
stringapi: Return a string reference for the configuration
stringapi: Use strings for feature arguments
stringapi: Pass strings as install directories in CPack
typo: Match argument name with the header
stringapi: Miscellaneous char* parameters
stringapi: Add string overload for the Def struct
stringapi: Use strings for directories
stringapi: Use strings for generator names
stringapi: Use strings for program paths
stringapi: Command names
stringapi: Use strings for cache iterator values
stringapi: Use strings for dependency information
speedup: Cache strings for comparisons
speedup: Avoid excess iterator dereferences
stringapi: Prevent a NULL dereference in WiX
CPackWiX: Fix test to build with expected config
Merge topic 'dev/string-apis' into next

fc5ba1f0 CPackWiX: Fix test to build with expected config
aee8464e stringapi: Prevent a NULL dereference in WiX
ea31d0e0 speedup: Avoid excess iterator dereferences
8228195f speedup: Cache strings for comparisons
10d6ac83 stringapi: Use strings for dependency information
6b3c3701 stringapi: Use strings for cache iterator values
76217b54 stringapi: Command names
43820d6f stringapi: Use strings for program paths
2e695d44 stringapi: Use strings for generator names
c88ddb0a stringapi: Use strings for directories
44cccc30 stringapi: Add string overload for the Def struct
d320ee82 stringapi: Miscellaneous char* parameters
06ca6668 typo: Match argument name with the header
b6df3ebc stringapi: Pass strings as install directories in CPack
ef42507a stringapi: Use strings for feature arguments
9aea0925 stringapi: Return a string reference for the configuration
...