Remove 64bit build designation on Solaris

- Revert commit c18852f650
- Remove -m64 from CMakeLists.txt by commit 08089a1b20
- Suggested by @andy-js in conversation https://github.com/libressl-portable/portable/pull/327

m4/check-os-options.m4

@@ -112,7 +112,6 @@ char buf[1]; getentropy(buf, 1);
 	*solaris*)
 		HOST_OS=solaris
 		HOST_ABI=elf
-		CFLAGS="$CFLAGS -m64"
 		CPPFLAGS="$CPPFLAGS -D__EXTENSIONS__ -D_XOPEN_SOURCE=600 -DBSD_COMP"
 		AC_SUBST([PLATFORM_LDADD], ['-lnsl -lsocket'])
 		;;