+ linking shared libraries, DSOs or programs.
+
+ shared_cppflags => Extra C preprocessor flags used when
+ processing C files for shared libraries.
+ shared_cflag => Extra C compiler flags used when compiling
+ for shared libraries, typically something
+ like "-fPIC".
+ shared_ldflag => Extra linking flags used when linking
+ shared libraries.
+ module_cppflags
+ module_cflags
+ module_ldflags => Has the same function as the corresponding
+ `shared_' attributes, but for building DSOs.
+ When unset, they get the same values as the
+ corresponding `shared_' attributes.