[builtins][test] Don't XFAIL divtc3_test.c on 32-bit Solaris/sparc fo… (#72403)

As detailed in Issue #72398, the recent builtins rework and
77d75dc caused `Builtins-sparc-sunos::
divtc3_test.c` to `XPASS` on 32-bit Solaris/SPARC. Since there are
several underlying issues, un-`XFAIL` the test for now until those are
resolved, to turn the Solaris/sparcv9 buildbot green again after 5 days.

Tested on `sparcv9-sun-solaris2.11` and `x86_64-pc-linux-gnu`.

Author: rorth

compiler-rt/test/builtins/Unit/divtc3_test.c

@@ -3,8 +3,8 @@
 // REQUIRES: c99-complex
 
 //
-// Bug 42493
-// XFAIL: sparc-target-arch
+// This test should be XFAILed on 32-bit sparc (sparc-target-arch, Issue
+// #41838), but that is currently hidden, which caused an XPASS (Issue #72398).
 //
 #include <stdio.h>