Fix undefined symbols in libpf_lib.so (#4312)

When I build `nav2_amcl` with `-Wl,--no-undefined` I noticed
`libpf_lib.so` has undefined symbols. This PR correctly links
`libpf_lib.so` to `libm` so all symbols can be found.

You can verify this by executing the following command:
```
ldd -r ./build/nav2_amcl/src/pf/libpf_lib.so
	linux-vdso.so.1 (0x00007ffd1f8c0000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x000074e909a00000)
	/lib64/ld-linux-x86-64.so.2 (0x000074e909e60000)
undefined symbol: ceil	(./build/nav2_amcl/src/pf/libpf_lib.so)
undefined symbol: atan2	(./build/nav2_amcl/src/pf/libpf_lib.so)
undefined symbol: sin	(./build/nav2_amcl/src/pf/libpf_lib.so)
undefined symbol: hypot	(./build/nav2_amcl/src/pf/libpf_lib.so)
undefined symbol: cos	(./build/nav2_amcl/src/pf/libpf_lib.so)
undefined symbol: log	(./build/nav2_amcl/src/pf/libpf_lib.so)
undefined symbol: sqrt	(./build/nav2_amcl/src/pf/libpf_lib.so)
undefined symbol: floor	(./build/nav2_amcl/src/pf/libpf_lib.so)
```

Signed-off-by: Ramon Wijnands <[email protected]>

Author: Rayman

nav2_amcl/src/pf/CMakeLists.txt

@@ -15,6 +15,7 @@ target_include_directories(pf_lib PRIVATE ../include)
 if(HAVE_DRAND48)
   target_compile_definitions(pf_lib PRIVATE "HAVE_DRAND48")
 endif()
+target_link_libraries(pf_lib m)
 
 install(TARGETS
   pf_lib