Tests: ignore GuardMalloc messages on all Apple build, not just XCode ones
GenerateExportHeader: Add newlines to separate the compiler output.

Make the error logs more readable.
Tests/IncludeDirectories: Avoid shared library with no symbols

The parent commit added a empty_entry_test shared library to the
IncludeDirectories test.  Some toolchains fail to create a shared
library with no user-defined symbols, so provide a dummy symbol.
GenerateExportHeader: Allow use of of this macro with MODULEs.

The significant issue with MODULEs is that on Windows, the exported
symbols must be dllexported and they are not imported.

In other export macro implementations this is done by defining an
export macro outside of any ifdef which depends on definitions set
on the command line. However, with cmake we already expect the
DEFINE_SYMBOL to be defined, so the regular EXPORT macro can be
used by such plugins.
Tests/Module/GenerateExportHeader: Test exported free-function
Add $<LINK_LANGUAGE> generator expression

They can't be used when evaluating link libraries, but they can be
used for include directories and compile definitions. Later they can
be used for compile options.
GenerateExportHeader: Generate only C identifiers as defines

The variables in this module are used to configure a header file
with defines whose name depends on the name of the target.

As valid names of targets may be invalid for use as defines, convert
the names of the defines used to C identifiers first. This is already
done in C++ code for the DEFINE_SYMBOL property.

This is not as simple as ensuring that the BASE_NAME is a C identifier,
because most of the define names are configurable, and because use of
a BASE_NAME which is not a C identifier, such as 4square can become a
C identifier by specifying a prefix in the generate_export_header
macro.
Merge topic 'Memchecker-Mac-fix'

0aed09f Tests: ignore GuardMalloc messages on all Apple build, not just XCode ones
Merge topic 'fix-include_directories-whitespace-handling'

a97240b Tests/IncludeDirectories: Avoid shared library with no symbols
Merge topic 'language-generator-expressions'

3241014 Add $<LINK_LANGUAGE> generator expression
Merge topic 'geh-output-tweak'

bb412d0 GenerateExportHeader: Add newlines to separate the compiler output.
Merge topic 'geh-add-missing-test'

74f24b2 Tests/Module/GenerateExportHeader: Test exported free-function
Merge topic 'geh-MODULE-export'

7ffef50 GenerateExportHeader: Allow use of of this macro with MODULEs.
Merge topic 'geh-cleanup-identifiers'

7e24997 GenerateExportHeader: Generate only C identifiers as defines