MDEV-26467: GCC 4.8.5 internal compiler error on ARMv8

We will disable some optimizations, because the function
row_ins_clust_index_entry_low() would fail to compile
ever since commit a73eedbf
changed the definition of srw_mutex::wr_unlock() to use
fetch_sub() instead of fetch_and().

For some reason, applying this work-around does not fix the
"could not split insn" error for that commit,
while it does work for
commit 277ba134.

storage/innobase/row/row0ins.cc

@@ -2501,6 +2501,13 @@ extern "C" int thd_is_slave(const MYSQL_THD thd);
 # define thd_is_slave(thd) 0
 #endif
 
+#if defined __aarch64__&&defined __GNUC__&&__GNUC__==4&&!defined __clang__
+/* Avoid GCC 4.8.5 internal compiler error due to srw_mutex::wr_unlock().
+We would only need this for row_ins_clust_index_entry_low(),
+but GCC 4.8.5 does not support pop_options. */
+# pragma GCC optimize ("no-expensive-optimizations")
+#endif
+
 /***************************************************************//**
 Tries to insert an entry into a clustered index, ignoring foreign key
 constraints. If a record with the same unique key is found, the other