Detect Broken ASTs rather than crashing.

[Keno]

No description provided.

[nkottary]

This could be an example:
julia> cxx""" #include """
true

julia> cxx""" void foo (int bar) { std::cout<< "Bar is :" << bar << std::endl } """
In file included from :1:
__cxxjl_4.cpp:1:65: error: expected ';' after expression
void foo (int bar) { std::cout<< "Bar is :" << bar << std::endl }
^
;
true

julia> cxx""" void foo (int bar) { std::cout<< "Bar is :" << bar << std::endl; } """
__cxxjl_5.cpp:1:7: error: redefinition of 'foo'
void foo (int bar) { std::cout<< "Bar is :" << bar << std::endl; }
^
__cxxjl_4.cpp:1:7: note: previous definition is here
void foo (int bar) { std::cout<< "Bar is :" << bar << std::endl }
^
true

julia>

However,
julia> jl_foo(a) = @cxx foo(a)
jl_foo (generic function with 1 method)

julia> jl_foo(5)
Bar is: 5

julia>