Factor extract_c_headers out of wrap_c_headers (no user-facing API change)
Factor extract_c_headers out of wrap_c_headers (no user-facing API change)

For interactive use

JuliaPackageMirrors/Clang.jl,mdcfrancis/Clang.jl,JuliaPackageMirrors/Clang.jl,mdcfrancis/Clang.jl,zhmz90/Clang.jl,ihnorton/Clang.jl,ihnorton/Clang.jl,zhmz90/Clang.jl