Fixes#208669
Issue :
With -flto, Fortran COMMON blocks larger than 4 GiB were silently
miscompiled. The linker reserved only the low 32 bits of the declared
size, so stores past that boundary could segfault with no diagnostic.
Root Cause :
storage::Uncommon::CommonSize in the LTO irsymtab was stored as 32-bit
(Word). Sizes above 2^32 bytes were truncated when the symtab was
written and read back at link time.
Fix :
Widen CommonSize to 64-bit and bump irsymtab format version to 4. Added
test to verify symtab records the full size.
