Fix malloc overflow check warning

To fix this warning:

../src/cairo-malloc-private.h:83:32: warning: comparison is always false due to limited range of data type [-Wtype-limits]
   83 |   ((size) != 0 && (size_t) (a) >= SIZE_MAX / (size_t) (size) ? NULL : \
      |                                ^~

Create two new macros to do the overflow checks:
_cairo_addl_size_t_overflow and _cairo_mul_size_t_overflow. Implement
them using compiler builtins where available.

Update cairo-malloc-private to use these fuctions and add an overflow
test to test the functions.

1 files changed, 1 insertions, 0 deletions

diff --git a/meson.build b/meson.build
index f10a0067b..7a0506712 100644
--- a/meson.build
+++ b/meson.build
@@ -151,6 +151,7 @@ check_headers = [
   ['fenv.h', {'check-funcs': ['feenableexcept', 'fedisableexcept', 'feclearexcept']}],
   ['xlocale.h'],
   ['sys/ioctl.h'],
+  ['intsafe.h'],
 ]
 
 check_types = [