[LyX/master] Fix compilation on gcc-15

[José Matos]

On Fri, 2025-01-17 at 10:08 +0100, Scott Kostyshak wrote:
> (next time) please put the warning/error output that GCC gives you in the
> commit message.
> 
> This way, when I am bisecting and I see that error, I can search in the LyX
> log and I know which commit I need to cherry-pick.
> 
> Thanks for the fix.
> 
> Scott

This was so simple. it is documented
https://gcc.gnu.org/gcc-15/porting_to.html#cxx

and even gcc suggests the right fix.

That was why this fell under the trivial fix.

For reference this is the error message:

mathed/MathParser.cpp: In function `std::ostream&
lyx::{anonymous}::operator<<(std::ostream&, const Token&)`:
mathed/MathParser.cpp:373:35: error: `uint32_t` does not name a type
  373 |                 os << static_cast<uint32_t>(t.character());
      |                                   ^~~~~~~~
mathed/MathParser.cpp:80:1: note: `uint32_t` is defined in header `<cstdint>`;
this is probably fixable by adding `#include <cstdint>`
   79 | #include "support/docstream.h"
  +++ |+#include <cstdint>
   80 | 
mathed/MathParser.cpp:375:42: error: `uint32_t` does not name a type
  375 |                 os << '[' << static_cast<uint32_t>(t.character()) << ','
<< t.cat() << ']';
      |                                          ^~~~~~~~
mathed/MathParser.cpp:375:42: note: `uint32_t` is defined in header `<cstdint>`;
this is probably fixable by adding `#include <cstdint>`
make[4]: *** [Makefile:2416: mathed/MathParser.o] Error 1

-- 
José Abílio