[Bug c/88568] [7/8/9 Regression] 'dllimport' no longer implies 'extern' in C

[10walls at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88568

--- Comment #22 from jon_y <10walls at gmail dot com> ---

Bootstrapped sucessfully on x86_64-pc-cygwin, test compiles and has the data
member dllimported. Patch looks good.