AppleClang does not support the cxx_thread_local feature, even
though it is based on a Clang version which does support the
feature.
http://stackoverflow.com/a/23850891/2428389
A possible reason for that is that thread_local might be used as
a variable in existing Apple SDK headers.
Extend the WriteCompilerDetectionHeader module to generate a define
for that feature with portability fallbacks. For the avoidance of
making it easy to write code which looks correct but which has odd
runtime behavior, don't set the define symbol at all if no
equivalent keyword is known.
Extend the write_compiler_detection_header interface to allow
specifying a location for supplementary files, and getting the
list of resulting files as a variable.
The DECL part is redundant, and the language part is not needed. The
source language and context already determines the language, so there
is no need to repeat it in the define name.
ddec418a Features: Add compiler version support to WriteCompilerDetectionHeader.
b7029576 Project: Add configurable name for version computation macros.
78acaafe Project: Separate simulated compiler id from version detection.
567af1a5 WCDH: Issue a better message for version compatibility.
Link to it from the documentation of related properties, variables
and commands.
Extend the cmake-developer(7) documentation with notes on
extending feature support for compilers.
Add properties and variables corresponding to CXX equivalents.
Add features for c_function_prototypes (C90), c_restrict (C99),
c_variadic_macros (C99) and c_static_assert (C11). This feature
set can be extended later.
Add a <PREFIX>_RESTRICT symbol define to WriteCompilerDetectionHeader
to conditionally represent the c_restrict feature.
Provide a function to write a portable header to detect compiler
features. Generate a preprocessor #error for unknown compilers
and compiler versions whose features are not yet recorded. This
error condition might be relaxed in the future, but for now it
is useful for verification of expectations.
Stephen Kelly
Brad King