[Issue 21946] New: importC: Support parsing __extension__ keyword

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21946

          Issue ID: 21946
           Summary: importC: Support parsing __extension__ keyword
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: ibuclaw at gdcproject.org

This keyword is used to suppress -pedantic warnings for many C extensions.
__extension__ has no effect aside from this.  In CParser, it should simply be
ignored.

---
__extension__ typedef long long __time64_t;
__extension__ typedef long long int64_t;
__extension__ typedef unsigned long long uint64_t;
__extension__ typedef long long int_least64_t;
__extension__ typedef unsigned long long uint_least64_t;
__extension__ typedef long long int_fast64_t;
__extension__ typedef unsigned long long uint_fast64_t;

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