Fix static build with mysql

When building static binaries, the order of libraries in the link command line
is significant. Use $LIBS for mysql libraries, so that mysql appear after the
object files that depends on it. This fixes build failures like the following.

/home/buildroot/build/instance-1/output/host/usr/bin/arm-linux-g++  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -Os  -static -static -I/home/buildroot/build/instance-1/output/host/usr/arm-buildroot-linux-uclibcgnueabi/sysroot/usr/include/mysql  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -Os  -static   -DUNIV_LINUX -DUNIV_LINUX  -static -static -rdynamic -L/home/buildroot/build/instance-1/output/host/usr/arm-buildroot-linux-uclibcgnueabi/sysroot/usr/lib -lmysqlclient_r -lz -lpthread -lcrypt -lnsl -lm -lpthread -o linknx linknx.o logger.o ruleserver.o objectcontroller.o eibclient.o threads.o timermanager.o persistentstorage.o xmlserver.o smsgateway.o emailgateway.o knxconnection.o services.o suncalc.o luacondition.o ioport.o ../ticpp/libticpp.a -L/home/buildroot/build/instance-1/output/host/usr/arm-buildroot-linux-uclibcgnueabi/sysroot/usr/lib -lpthsem    -lm -largp
persistentstorage.o: In function `MysqlPersistentStorage::~MysqlPersistentStorage()':
persistentstorage.cpp:(.text+0x2c): undefined reference to `mysql_close'
persistentstorage.o: In function `MysqlPersistentStorage::MysqlPersistentStorage(ticpp::Element*)':
persistentstorage.cpp:(.text+0x518): undefined reference to `mysql_init'
persistentstorage.cpp:(.text+0x570): undefined reference to `mysql_options'
persistentstorage.cpp:(.text+0x5a8): undefined reference to `mysql_real_connect'
persistentstorage.cpp:(.text+0x5c0): undefined reference to `mysql_options'
persistentstorage.cpp:(.text+0x618): undefined reference to `mysql_error'
persistentstorage.cpp:(.text+0x6c0): undefined reference to `mysql_options'
persistentstorage.o: In function `MysqlPersistentStorage::write(std::string const&, std::string const&)':
persistentstorage.cpp:(.text+0xb70): undefined reference to `mysql_real_query'
persistentstorage.cpp:(.text+0xbcc): undefined reference to `mysql_error'
persistentstorage.o: In function `MysqlPersistentStorage::read(std::string const&, std::string const&)':
persistentstorage.cpp:(.text+0xd14): undefined reference to `mysql_real_query'
persistentstorage.cpp:(.text+0xd38): undefined reference to `mysql_store_result'
persistentstorage.cpp:(.text+0xd40): undefined reference to `mysql_num_rows'
persistentstorage.cpp:(.text+0xd50): undefined reference to `mysql_fetch_row'
persistentstorage.cpp:(.text+0xd68): undefined reference to `mysql_free_result'
persistentstorage.cpp:(.text+0xdc8): undefined reference to `mysql_error'
persistentstorage.o: In function `MysqlPersistentStorage::writelog(std::string const&, std::string const&)':
persistentstorage.cpp:(.text+0xf74): undefined reference to `mysql_real_query'
persistentstorage.cpp:(.text+0xfd0): undefined reference to `mysql_error'
collect2: error: ld returned 1 exit status

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
---
Patch status: sent to jef2000@users.sourceforge.net

diff -Nuar linknx-0.0.1.32-orig/acinclude.m4 linknx-0.0.1.32/acinclude.m4
--- linknx-0.0.1.32-orig/acinclude.m4	2011-01-09 16:47:32.000000000 +0200
+++ linknx-0.0.1.32/acinclude.m4	2016-03-15 12:41:19.983861719 +0200
@@ -36,7 +36,7 @@
     CFLAGS="$CFLAGS $ADDFLAGS"    
     CXXFLAGS="$CXXFLAGS $ADDFLAGS"    
 
-    LDFLAGS="$LDFLAGS "`$MYSQL_CONFIG --libs_r`
+    LIBS="$LIBS "`$MYSQL_CONFIG --libs_r`
     
     AC_MSG_RESULT($MYSQL_CONFIG)
 	AC_DEFINE([HAVE_MYSQL], [1], [Build with MySQL support.])