COMPILE_DEFINITIONS
-------------------

Preprocessor definitions for compiling a target's sources.

The COMPILE_DEFINITIONS property may be set to a semicolon-separated
list of preprocessor definitions using the syntax VAR or VAR=value.
Function-style definitions are not supported.  CMake will
automatically escape the value correctly for the native build system
(note that CMake language syntax may require escapes to specify some
values).  This property may be set on a per-configuration basis using
the name COMPILE_DEFINITIONS_<CONFIG> where <CONFIG> is an upper-case
name (ex.  "COMPILE_DEFINITIONS_DEBUG").

CMake will automatically drop some definitions that are not supported
by the native build tool.  The VS6 IDE does not support definition
values with spaces (but NMake does).

Contents of COMPILE_DEFINITIONS may use "generator expressions" with
the syntax "$<...>".  Generator expressions are evaluated during build
system generation to produce information specific to each build
configuration.  Valid expressions are:

::

  $<0:...>                  = empty string (ignores "...")
  $<1:...>                  = content of "..."
  $<CONFIG:cfg>             = '1' if config is "cfg", else '0'
  $<CONFIGURATION>          = configuration name
  $<BOOL:...>               = '1' if the '...' is true, else '0'
  $<STREQUAL:a,b>           = '1' if a is STREQUAL b, else '0'
  $<ANGLE-R>                = A literal '>'. Used to compare strings which contain a '>' for example.
  $<COMMA>                  = A literal ','. Used to compare strings which contain a ',' for example.
  $<SEMICOLON>              = A literal ';'. Used to prevent list expansion on an argument with ';'.
  $<JOIN:list,...>          = joins the list with the content of "..."
  $<TARGET_NAME:...>        = Marks ... as being the name of a target.  This is required if exporting targets to multiple dependent export sets.  The '...' must be a literal name of a target- it may not contain generator expressions.
  $<INSTALL_INTERFACE:...>  = content of "..." when the property is exported using install(EXPORT), and empty otherwise.
  $<BUILD_INTERFACE:...>    = content of "..." when the property is exported using export(), or when the target is used by another target in the same buildsystem. Expands to the empty string otherwise.
  $<PLATFORM_ID>            = The CMake-id of the platform   $<PLATFORM_ID:comp>       = '1' if the The CMake-id of the platform matches comp, otherwise '0'.
  $<C_COMPILER_ID>          = The CMake-id of the C compiler used.
  $<C_COMPILER_ID:comp>     = '1' if the CMake-id of the C compiler matches comp, otherwise '0'.
  $<CXX_COMPILER_ID>        = The CMake-id of the CXX compiler used.
  $<CXX_COMPILER_ID:comp>   = '1' if the CMake-id of the CXX compiler matches comp, otherwise '0'.
  $<VERSION_GREATER:v1,v2>  = '1' if v1 is a version greater than v2, else '0'.
  $<VERSION_LESS:v1,v2>     = '1' if v1 is a version less than v2, else '0'.
  $<VERSION_EQUAL:v1,v2>    = '1' if v1 is the same version as v2, else '0'.
  $<C_COMPILER_VERSION>     = The version of the C compiler used.
  $<C_COMPILER_VERSION:ver> = '1' if the version of the C compiler matches ver, otherwise '0'.
  $<CXX_COMPILER_VERSION>   = The version of the CXX compiler used.
  $<CXX_COMPILER_VERSION:ver> = '1' if the version of the CXX compiler matches ver, otherwise '0'.
  $<TARGET_FILE:tgt>        = main file (.exe, .so.1.2, .a)
  $<TARGET_LINKER_FILE:tgt> = file used to link (.a, .lib, .so)
  $<TARGET_SONAME_FILE:tgt> = file with soname (.so.3)

where "tgt" is the name of a target.  Target file expressions produce
a full path, but _DIR and _NAME versions can produce the directory and
file name components:

::

  $<TARGET_FILE_DIR:tgt>/$<TARGET_FILE_NAME:tgt>
  $<TARGET_LINKER_FILE_DIR:tgt>/$<TARGET_LINKER_FILE_NAME:tgt>
  $<TARGET_SONAME_FILE_DIR:tgt>/$<TARGET_SONAME_FILE_NAME:tgt>



::

  $<TARGET_PROPERTY:tgt,prop>   = The value of the property prop on the target tgt.

Note that tgt is not added as a dependency of the target this
expression is evaluated on.

::

  $<TARGET_POLICY:pol>          = '1' if the policy was NEW when the 'head' target was created, else '0'.  If the policy was not set, the warning message for the policy will be emitted.  This generator expression only works for a subset of policies.
  $<INSTALL_PREFIX>         = Content of the install prefix when the target is exported via INSTALL(EXPORT) and empty otherwise.

Boolean expressions:

::

  $<AND:?[,?]...>           = '1' if all '?' are '1', else '0'
  $<OR:?[,?]...>            = '0' if all '?' are '0', else '1'
  $<NOT:?>                  = '0' if '?' is '1', else '1'

where '?' is always either '0' or '1'.

Expressions with an implicit 'this' target:

::

  $<TARGET_PROPERTY:prop>   = The value of the property prop on the target on which the generator expression is evaluated.

Disclaimer: Most native build tools have poor support for escaping
certain values.  CMake has work-arounds for many cases but some values
may just not be possible to pass correctly.  If a value does not seem
to be escaped correctly, do not attempt to work-around the problem by
adding escape sequences to the value.  Your work-around may break in a
future version of CMake that has improved escape support.  Instead
consider defining the macro in a (configured) header file.  Then
report the limitation.  Known limitations include:

::

  #          - broken almost everywhere
  ;          - broken in VS IDE 7.0 and Borland Makefiles
  ,          - broken in VS IDE
  %          - broken in some cases in NMake
  & |        - broken in some cases on MinGW
  ^ < > \"   - broken in most Make tools on Windows

CMake does not reject these values outright because they do work in
some cases.  Use with caution.
