This fixes issue where empty and unallocated sections are left without
a VMA. Some relocations depend on the section VMA being set even if there
is no data there, as the binary can refer to the symbols. Linker defined
symbols do not contain data -> they can produce empty sections.
This issue is seen when building a loadable file which declares _sctors /
_sdtors linker defined symbols for ctor/dtor sections which are empty.
crt0 references these symbols, so they need to be relocated, but the
section VMA is not set -> they go outside of the addressable range of the
user binary causing a potential crash.
e384a6a625