[Bug bootstrap/58289] gcc/gengtype.c includes gcc/double-int.h, which uses C++ constructs

[jklowden at schemamania dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58289

--- Comment #2 from James K. Lowden <jklowden at schemamania dot org> ---
(In reply to Andrew Pinski from comment #1)
> GCC is now a C++ program even though it uses the .c file extension.  Use
> clang in C++ mode instead.

Thank you, but the the problem is not completely solved.  

1.  This is not mentioned anywhere in
http://gcc.gnu.org/install/configure.html. 
2.  Not all .c files needed to build gcc are C++.  Setting Clang to compile 
all files as C++ means libiberty cannot be compiled:

../../../libiberty/sha1.c:235:11: error: '<anonymous struct at
../../../libiberty/sha1.c:235:11>' can not be defined in a type specifier

The compiler has precious little information to tell it what language to use.  
How to distinguish between C and C++ if not by the extension?  Particularly in 
a project with both C and C++ source files among its build-time dependencies?