The demangle-rust.vgtest would fail because the demangle-rust binary
wasn't build by default. Add it to check_PROGRAMS and define
demangle_rust_SOURCES to make sure it is always build.
custom_alloc \
custom-overlap \
demangle \
+ demangle-rust \
big_debuginfo_symbol \
deep-backtrace \
describe-block \
leak_cpp_interior_SOURCES = leak_cpp_interior.cpp
demangle_SOURCES = demangle.cpp
+demangle_rust_SOURCES = demangle-rust.c
# Suppress various gcc warnings which are correct, but for things
# we are actually testing for at runtime.