glibc patch: add backwards compatibility for some symbols

- `fcntl` was renamed to `fcntl64` in glibc 2.28 (see #9485)
- `res_{,n}{search,query,querydomain}` became "their own" symbols since
  glibc 2.34: they were prefixed with `__` before.

This PR makes it possible to use `fcntl` with glibc 2.27 or older and
the `res_*` functions with glibc 2.33 or older.

These patches will become redundant with universal-headers and can be
dropped. But we have to do with what we have now.

lib/libc/include/generic-glibc/fcntl.h

@@ -167,6 +167,11 @@ typedef __pid_t pid_t;
 					   effective IDs, not real IDs.  */
 #endif
 
+
+/* fcntl was a simple symbol until glibc 2.27 inclusive.
+ * glibc 2.28 onwards converted it to a macro when compiled with
+ * USE_LARGEFILE64. */
+#if (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 28) || __GLIBC__ > 2
 /* Do the file control operation described by CMD on FD.
    The remaining arguments are interpreted depending on CMD.
 
@@ -197,6 +202,9 @@ extern int __fcntl_time64 (int __fd, int __request, ...) __THROW;
 #  define fcntl __fcntl_time64
 # endif
 #endif
+#else /* glibc 2.27 or lower */
+extern int fcntl (int __fd, int __cmd, ...);
+#endif
 
 /* Open FILE and return a new file descriptor for it, or -1 on error.
    OFLAG determines the type of access used.  If O_CREAT or O_TMPFILE is set

lib/libc/include/generic-glibc/resolv.h

@@ -170,6 +170,28 @@ __END_DECLS
 #define res_init		__res_init
 #define res_isourserver		__res_isourserver
 
+/* In glibc 2.33 and earlier res_search, res_nsearch, res_query, res_nquery,
+ * res_querydomain, res_nquerydomain were #define'd to __res_search,
+ * __res_nsearch, etc. glibc 2.34 onwards removes the macros and exposes the
+ * symbols directly. New glibc exposes compat symbols with underscores for
+ * backwards compatibility. Applications linked to glibc 2.34+ are expected
+ * to use the non-underscored symbols.
+ *
+ * It will be enough to bring the macros back when compiling against the older
+ * glibc versions.
+ *
+ * See glibc commit ea9878ec271c791880fcbbe519d70c42f8113750.
+ */
+#if (__GLIBC__ == 2 && __GLIBC_MINOR__ < 34)
+#define res_search        __res_search
+#define res_nsearch       __res_nsearch
+#define res_query         __res_query
+#define res_nquery        __res_nquery
+#define res_querydomain   __res_querydomain
+#define res_nquerydomain  __res_nquerydomain
+#endif
+/* end glibc compat hacks */
+
 #ifdef _LIBC
 # define __RESOLV_DEPRECATED
 # define __RESOLV_DEPRECATED_MSG(msg)