[Bug target/102353] New: powerpc64le-linux-gnu build failure when build != host

[sandra at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102353

            Bug ID: 102353
           Summary: powerpc64le-linux-gnu build failure when build != host
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sandra at gcc dot gnu.org
                CC: wschmidt at linux dot ibm.com
  Target Milestone: ---
              Host: powerpc64le-linux-gnu
            Target: powerpc64le-linux-gnu
             Build: x86_64-linux-gnu

I'm trying to build gcc for powerpc64le-linux-gnu host and target from
x86_64-linux-gnu host using scripts that have been known to work within the
last month or so.  I'm seeing multiple linker errors like 

ld: rs6000-gen-builtins.o: Relocations in generic ELF (EM: 21)

followed by

ld: rs6000-gen-builtins.o: error adding symbols: file in wrong format

And indeed, looking at config/rs6000/t-rs6000, this seems to be broken:

rs6000-gen-builtins.o: $(srcdir)/config/rs6000/rs6000-gen-builtins.c
        $(COMPILE) $<
        $(POSTCOMPILE)

rbtree.o: $(srcdir)/config/rs6000/rbtree.c
        $(COMPILE) $<
        $(POSTCOMPILE)

rs6000-gen-builtins: rs6000-gen-builtins.o rbtree.o
        $(LINKER_FOR_BUILD) $(BUILD_LINKERFLAGS) $(BUILD_LDFLAGS) -o $@ \
            $(filter-out $(BUILD_LIBDEPS), $^) $(BUILD_LIBS)

The two .o files are being built with the *host* compiler, and we're trying to
link them with the *build* linker.  ???