If: Introduce policy CMP0054 - don't dereference quoted variables in if()
Modules/Test*.cmake: Use if(DEFINED) to simplify conditions

Replace old hacks of the form 'if("${VAR}" MATCHES "^${VAR}$")'
with the much simpler 'if(NOT DEFINED ${VAR})'.
FindGTK2: Avoid depending on if() to dereference a quoted variable

Explicitly dereference GTK2_${_var}CONFIG_INCLUDE_DIR and
GTK2_${_var}_INCLUDE_DIR when comparing their values.
libarchive: Avoid depending on if() to dereference a quoted variable
cmcurl: Use if(DEFINED) to simplify conditions

Replace old hacks of the form 'if("${VAR}" MATCHES "^${VAR}$")'
with the much simpler 'if(NOT DEFINED ${VAR})'.
FPHSA: Avoid if() dereferencing of quoted variable

Legacy invocations may pass a variable name where "DEFAULT_MSG" belongs.
When comparing FPHSA_FAIL_MESSAGE to "DEFAULT_MSG", use a leading "x" on
both sides to avoid mistaking the value of the message for a variable
name.
Fix if() checks of CMAKE_SYSTEM_NAME on Cygwin

The CMAKE_SYSTEM_NAME is "CYGWIN", but we also define a variable
named "CYGWIN" to "1".  Avoid allowing if() to expand the "CYGWIN"
string as a variable.
Merge topic 'if-sanity' into next

da23efc8 Fix if() checks of CMAKE_SYSTEM_NAME on Cygwin
6e99d9ed FPHSA: Avoid if() dereferencing of quoted variable
808af1e5 cmcurl: Use if(DEFINED) to simplify conditions
1ed1c906 libarchive: Avoid depending on if() to dereference a quoted variable
73298c2a FindGTK2: Avoid depending on if() to dereference a quoted variable
81956fba Modules/Test*.cmake: Use if(DEFINED) to simplify conditions
5922fc2c If: Introduce policy CMP0054 - don't dereference quoted variables in if()