puzzles: Ensure to link against libm for math functions

Without this we can see failures like:

| make: *** [samegame] Error 1
| /media/build1/poky/build/tmp/sysroots/x86_64-linux/usr/libexec/i586-poky-linux/gcc/i586-poky-linux/4.6.3/ld: inertia.o: undefined reference to symbol 'sqrt@@GLIBC_2.0'
| /media/build1/poky/build/tmp/sysroots/x86_64-linux/usr/libexec/i586-poky-linux/gcc/i586-poky-linux/4.6.3/ld: note: 'sqrt@@GLIBC_2.0' is defined in DSO /media/build1/poky/build/tmp/sysroots/qemux86/lib/libm.so.6 so try adding it to the linker command line
| /media/build1/poky/build/tmp/sysroots/qemux86/lib/libm.so.6: could not read symbols: Invalid operation
| collect2: ld returned 1 exit status
| make: *** [inertia] Error 1

(From OE-Core rev: 2ebfb9d9ed7554180c3c077b14291a1853f8e2ef)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-sato/puzzles/puzzles_r9306.bb

@@ -2,7 +2,7 @@ DESCRIPTION="Simon Tatham's Portable Puzzle Collection"
 HOMEPAGE="http://www.chiark.greenend.org.uk/~sgtatham/puzzles/"
 
 DEPENDS = "gtk+ libxt"
-PR = "r0"
+PR = "r1"
 MOD_PV = "${@d.getVar('PV',1)[1:]}"
 
 LICENSE = "MIT"
@@ -23,6 +23,7 @@ do_configure () {
 
 do_compile_prepend = " \
         export XLDFLAGS='${LDFLAGS} `${STAGING_BINDIR_NATIVE}/pkg-config gtk+-2.0 --libs`'; \
+        export XLFLAGS=-lm \
 	export CFLAGS='${CFLAGS} -I./ `${STAGING_BINDIR_NATIVE}/pkg-config gtk+-2.0 --cflags`'; "
 
 FILES_${PN} = "${prefix}/games/* ${datadir}/applications/*"