[fix](be) Gate resolv_shim to glibc >= 2.34 to fix CI -Winfinite-recursion

On glibc < 2.34 (e.g. the AlmaLinux 8 / glibc 2.28 CI build image),
<resolv.h> #defines res_nsearch as __res_nsearch, so the forwarder body
called itself and clang -Werror -Winfinite-recursion broke the BE UT and
COMPILE checks. The shim is only needed on glibc >= 2.34 anyway (older
glibc still exports __res_nsearch as a default-versioned symbol), so gate
it with __GLIBC_PREREQ(2, 34) and keep the translation unit non-empty for
-Wpedantic.

Author: u70b3

be/src/glibc-compatibility/CMakeLists.txt

@@ -57,7 +57,8 @@ if (GLIBC_COMPATIBILITY)
     # libcalls. Workaround: Use object file so that linker will always take a
     # look at its symbol table.
     list(REMOVE_ITEM glibc_compatibility_sources musl/getrandom.c)
-    # NOTE: the OBJECT lib must always provide the resolv_shim symbol; keep it out of the archive.
+    # NOTE: the OBJECT lib must always provide the resolv_shim symbol where it
+    # exists (resolv_shim.c is a no-op on glibc < 2.34); keep it out of the archive.
     list(REMOVE_ITEM glibc_compatibility_sources resolv_shim.c)
     # NOTE(amos): sanitizers might generate memcpy references that are too late to
     # refer. Let's also extract memcpy definitions explicitly to avoid UNDEF GLIBC 2.14.

be/src/glibc-compatibility/resolv_shim.c

@@ -22,11 +22,27 @@
 // on Ubuntu 22.04 (glibc 2.35). Provide a thin forwarder to the public
 // res_nsearch entry point, which is the identical implementation (same
 // symbol address in libc).
+//
+// The shim must only exist where it is needed: on glibc < 2.34,
+// __res_nsearch is still a default-versioned libc symbol, and <resolv.h>
+// there #defines res_nsearch as __res_nsearch, which would fold the
+// forwarder below into infinite self-recursion (clang -Winfinite-recursion
+// errors out under -Werror, e.g. on the AlmaLinux 8 / glibc 2.28 CI image).
 
 #include <resolv.h>
 #include <sys/types.h>
 
+#if defined(__GLIBC__) && __GLIBC_PREREQ(2, 34)
+
 int __res_nsearch(res_state statp, const char* dname, int class_, int type,
                   unsigned char* answer, int anslen) {
     return res_nsearch(statp, dname, class_, type, answer, anslen);
 }
+
+#else
+
+// Keep the translation unit non-empty (-Wpedantic forbids an empty one);
+// no shim is required on glibc < 2.34.
+typedef int doris_resolv_shim_unused_t;
+
+#endif