[Bug c++/115797] [15 Regression] 'extern "C" { #include <math.h> }' fails with 'error: template with C linkage' since r15-1857-gde19b516edbf91

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115797

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Doing this is undefined (and annoying).

[using.headers] in the standard says "A translation unit shall include a header
only outside of any declaration or definition"