## Why
Currently, the following does not work when compiled with clang:
```c++
#include <cmath>
struct ConvertibleToFloat {
operator float();
};
bool test(ConvertibleToFloat x) {
return std::isnormal(x);
}
```
See https://godbolt.org/z/5bos8v67T for differences with respect to
msvc, gcc or icx. It fails for `float`, `double` and `long double` (all
cv-unqualified floating-point types).
## What
Test and provide overloads as expected by the ISO C++ standard. The
classification/comparison function `isnormal` is defined since C++11
until C++23 as
```c++
bool isnormal( float num );
bool isnormal( double num );
bool isnormal( long double num );
```
and since C++23 as
```c++
constexpr bool isnormal( /* floating-point-type */ num );
```
for which "the library provides overloads for all cv-unqualified
floating-point types as the type of the parameter num". See §28.7.1/1 in
the [ISO C++
standard](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/n4950.pdf)
or check
[cppreference](https://en.cppreference.com/w/cpp/numeric/math/isnormal).
First, fix a collision with the Point type from MacTypes.h, which was
reported on Slack, 2022-07-31: https://cpplang.slack.com/archives/C2X659D1B/p1659284691275889
Second, rename the meta:: namespace to types::. OSX's "/usr/include/ncurses.h"
defines a `meta` function, and is (for some reason) included in
"<SDK>/usr/include/module.modulemap", so that identifier is off-limits
for us to use in anything that compiles with -fmodules:
libcxx/test/support/type_algorithms.h:16:11: error: redefinition of 'meta' as different kind of symbol
namespace meta {
^
<SDK>/usr/include/ncurses.h:603:28: note: previous definition is here
extern NCURSES_EXPORT(int) meta (WINDOW *,bool); /* implemented */
^
Finally, add a CI configuration for modules on OS X to make sure it
does not regress.
Differential Revision: https://reviews.llvm.org/D144915
