Makefile: fix cross-compiling the server

MySQL Makefile believes it can run code it just compiled, to
generate a header. This does not work for cross-compilation.

Instead, use a pre-installed host-version of the required tool.

Signed-off-by: Marcelo Gutierrez (UTN/FRH) <kuyurix@gmail.com>

--- mysql-5.1.70/sql/Makefile.am
+++ mysql-5.1.70.patch/sql/Makefile.am
@@ -177,7 +177,7 @@
 # this avoid the rebuild of the built files in a source dist
 lex_hash.h:	gen_lex_hash.cc lex.h
 		$(MAKE) $(AM_MAKEFLAGS) gen_lex_hash$(EXEEXT)
-		./gen_lex_hash$(EXEEXT) > $@-t
+		gen_lex_hash$(EXEEXT) > $@-t
 		$(MV) $@-t $@
 
 # For testing of udf_example.so

--- mysql-5.1.70/sql/Makefile.in
+++ mysql-5.1.70.patch/sql/Makefile.in
@@ -1310,7 +1310,7 @@
 # this avoid the rebuild of the built files in a source dist
 lex_hash.h:	gen_lex_hash.cc lex.h
 		$(MAKE) $(AM_MAKEFLAGS) gen_lex_hash$(EXEEXT)
-		./gen_lex_hash$(EXEEXT) > $@-t
+		gen_lex_hash$(EXEEXT) > $@-t
 		$(MV) $@-t $@
 
 # We might have some stuff not built in this build, but that we want to install