I decided I wanted to upgrade my kernel from the 1.5Q one to whatever's
in current (among other things, I wanted to see if the keyboard sync
problem has been fixed).

I sup'ed all of current and proceeded to make build (after upgrading
make and yacc)

I ran into two problems, one of which I cannot figure out how to solve.
I'm aware that current is "not guaranteed to work, or even build", but
I'm asking about it anyway on the off chance that a) someone will see
what stupid thing I'm doing or b) something really is broken, but no one
knows about it

The first problem happens when building libc:
building shared c library (version 12.71)
ld -x -shared -soname libc.so.12 -o libc.so.12.71  /usr/lib/crtbeginS.o 
--whole
-archive libc_pic.a --no-whole-archive   /usr/lib/crtendS.o
libc_pic.a(__posix_rename.so): In function `___posix_rename':
__posix_rename.so(.text+0x1c): relocation truncated to fit:
R_SPARC_GOT13 ___cerror
[more of same...]
This seems to be caused by /usr/include/sparc64/asm.h being confused
when it's included by something being run under /usr/bin/cpp, rather
than gcc -E. since __arch64__ is not defined by the standalone
preprocessor, _C_LABEL is defined in the pre-ELF (prefix C symbols with
_) way of doing things. I have worked around this for my build.

The second problem happens the first time a program is built. It seems
that there is something wrong with one or more of the crt*.o files
instaled into /usr/lib, and most any program built with them segfaults.
This may have to do with environment setup, but given the unhappy stack,
I can't tell for sure:
(gdb) b main
Breakpoint 1 at 0x1005d0: file foo.c, line 3.
(gdb) run
Starting program: /home/cg2v/foo 

Breakpoint 1, main (argc=0, argv=0xffffffffffffd548, envp=0x7ffffd550)
    at foo.c:3
3       printf("I don't care what my arguments are\n");
(gdb) cont
Continuing.

Program received signal SIGSEGV, Segmentation fault.
0x108d5c in __findenv ()
(gdb) where
#0  0x108d5c in __findenv ()