MDEV-135: work-around a GCC bug seen on Debian 5 "lenny" 64-bit.

debian/dist/Debian/rules

@@ -66,7 +66,7 @@ endif
 	( test -d $(builddir) || mkdir $(builddir) ) && cd $(builddir) && \
 	sh -c 'PATH=$${MYSQL_BUILD_PATH:-"/bin:/usr/bin:/usr/local/bin"} \
 			CC=$${MYSQL_BUILD_CC:-gcc} \
-			CFLAGS=$${MYSQL_BUILD_CFLAGS:-"-O2 -fno-omit-frame-pointer -g -pipe -Wall -Wno-uninitialized"} \
+			CFLAGS=$${MYSQL_BUILD_CFLAGS:-"-O2 -fno-omit-frame-pointer -g -pipe -Wall -Wno-uninitialized $$(case `lsb_release -sc` in (lenny) echo -DWORKAROUND_GCC_4_3_2_BUG ;; esac)"} \
 			CXX=$${MYSQL_BUILD_CXX:-g++} \
 			CXXFLAGS=$${MYSQL_BUILD_CXXFLAGS:-"-O2 -fno-omit-frame-pointer -g -pipe -Wall -Wno-uninitialized"} \
 		cmake .. \

sql/item_sum.cc

@@ -1647,7 +1647,7 @@ double Item_sum_avg::val_real()
 
 my_decimal *Item_sum_avg::val_decimal(my_decimal *val)
 {
-  my_decimal sum_buff, cnt;
+  my_decimal cnt;
   const my_decimal *sum_dec;
   DBUG_ASSERT(fixed == 1);
   if (aggr)

strings/decimal.c

@@ -2293,7 +2293,11 @@ static int do_div_mod(const decimal_t *from1, const decimal_t *from2,
       DBUG_ASSERT(buf0 < to->buf + to->len);
       *buf0=(dec1)guess;
     }
+#ifdef WORKAROUND_GCC_4_3_2_BUG
+    dcarry= *(volatile dec1 *)start1;
+#else
     dcarry= *start1;
+#endif
     start1++;
   }
   if (mod)