update libelf from elftoolchain r3717 to r3833

ok deraadt@

do not use plain-text ELF(3) to reference page titles, use .Nm or .Xr.:
issue noticed by naddy@ when he inspected a bug report from aalm@;
while here, use .At where appropriate;
OK naddy@ jmc@

add libelf from elftoolchain r3669

A 2 clause BSD licensed implementation of the SVR4 ELF API also
implemented by mr511.de libelf (devel/libelf in ports) and elfutils.

It is being added to base to

add libelf from elftoolchain r3669

A 2 clause BSD licensed implementation of the SVR4 ELF API also
implemented by mr511.de libelf (devel/libelf in ports) and elfutils.

It is being added to base to allow Mesa to use it in future.

shlib major is higher than devel/libelf and pkg-config version is 0.8.2
to pass a glib2 configure test so this can replace the use of
devel/libelf in ports.

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