Build failure on OpenBSD-6.4 the the following:
rts/RtsSymbols.c:994:1: error: error: redefinition of '_DYNAMIC' as different kind of symbol | 994 | RTS_OPENBSD_ONLY_SYMBOLS | ^ RTS_OPENBSD_ONLY_SYMBOLS ^
On OpenBSD _DYNAMIC was always defined in <elf.h> headers
but used not to be included.
The change explicitly includes <elf.h> as a source of symbol definition.
Signed-off-by: Sergei Trofimovich <firstname.lastname@example.org>