Do not build sparc32 libgcc functions into static libc

Since GCC commit f31a019d1161ec78846473da743aedf49cca8c27 "Emit
funcall external declarations only if actually used.", the glibc
testsuite has failed to build for 32-bit SPARC with GCC mainline.

/scratch/jmyers/glibc-bot/install/compilers/sparc64-linux-gnu/lib/gcc/sparc64-glibc-linux-gnu/14.0.0/../../../../sparc64-glibc-linux-gnu/bin/ld: /scratch/jmyers/glibc-bot/install/compilers/sparc64-linux-gnu/lib/gcc/sparc64-glibc-linux-gnu/14.0.0/32/libgcc.a(_divsi3.o): in function `.div':
/scratch/jmyers/glibc-bot/src/gcc/libgcc/config/sparc/lb1spc.S:138: multiple definition of `.div'; /scratch/jmyers/glibc-bot/build/glibcs/sparcv9-linux-gnu/glibc/libc.a(sdiv.o):/scratch/jmyers/glibc-bot/src/glibc/gnulib/../sysdeps/sparc/sparc32/sparcv9/sdiv.S:13: first defined here
/scratch/jmyers/glibc-bot/install/compilers/sparc64-linux-gnu/lib/gcc/sparc64-glibc-linux-gnu/14.0.0/../../../../sparc64-glibc-linux-gnu/bin/ld: disabling relaxation; it will not work with multiple definitions
collect2: error: ld returned 1 exit status
make[3]: *** [../Rules:298: /scratch/jmyers/glibc-bot/build/glibcs/sparcv9-linux-gnu/glibc/nptl/tst-cancel24-static] Error 1

https://sourceware.org/pipermail/libc-testresults/2023q4/012154.html

I'm not sure of the exact sequence of undefined references that cause
first the glibc object file defining .div and then the libgcc object
file defining both .div and .udiv to be pulled in (which must have
been perturbed by that GCC change in a way that introduced the build
failure), but I think the failure illustrates that it's inherently
fragile for glibc to define symbols in separate object files that
libgcc defines in the same object file - and indeed for glibc to
redefine libgcc symbols at all, since the division into object files
shouldn't really be part of the interface between libgcc and libc.

These symbols appear to be in libc only for compatibility, maybe one
of the cases where they were accidentally exported from shared libc in
glibc 2.0 before the introduction of symbol versioning and so programs
started expecting shared libc to provide them.  Thus, there is no need
to have them in static libc.  Add this set of libgcc functions to
shared-only-routines so they are no longer provided in static libc.
(No change is made regarding .mul - dotmul source file - since unlike
the other symbols in this grouping, it doesn't actually appear to be a
libgcc symbol, at least in current GCC.)

Tested with build-many-glibcs.py for sparcv9-linux-gnu with GCC
mainline.

sysdeps/sparc/sparc32/Makefile

@@ -17,6 +17,7 @@
 
 ifeq ($(subdir),gnulib)
 sysdep_routines = dotmul umul $(divrem) alloca
+shared-only-routines += umul $(divrem)
 endif	# gnulib
 
 divrem := sdiv udiv rem urem