spec: Set EXTRA_CXXFLAGS for perf demangle-cxx.o
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2233269
Commit 65cd8e55 started gating demangle-cxx.o on CONFIG_CXX_DEMANGLE, but the related cxa-demangle feature test was failing due to missing PIE, needed by rpm LDFLAGS. Setting EXTRA_CXXFLAGS gets them back in alignment.
This fixes Rust demangling, because that depends on the initial C++ demangling pass to handle the common parts of the format.
Signed-off-by: Josh Stone jistone@redhat.com