Fix compiler flags.

In particular, do not overwrite CFLAGS and use LDFLAGS instead of CFLAGS during
linking.

Based on the Debian patch:
http://sources.debian.net/src/wmbubble/1.51-1/debian/patches/fix-compiler-flags.patch/
Fix -Wformat compiler warnings.

In particular, several like:
bubblemon.c: In function ‘render_secondary’:
bubblemon.c:1009:4: warning: format ‘%llu’ expects argument of type ‘long long unsigned int’, but argument 4 has type ‘u_int64_t’ [-Wformat=]
    snprintf(number, 8, "%6lluM", bm.mem_used >> 20);
    ^
and
bubblemon.c: In function ‘make_new_bubblemon_dockapp’:
bubblemon.c:620:2: warning: format ‘%u’ expects argument of type ‘unsigned int *’, but argument 3 has type ‘int *’ [-Wformat=]
  sscanf(datefont_xpm[0],"%u %u %u %u",&maxwidth,&yy,&datefont_offset,&cc);
  ^
Fix -Wpedantic compiler warnings.

In particular:
In file included from bubblemon.c:66:0:
include/bubblemon.h:84:54: warning: extra semicolon in struct or union specified [-Wpedantic]
     unsigned char bubblebuf[BOX_SIZE * (BOX_SIZE+4)];;
and
bubblemon.c: In function ‘main’:
bubblemon.c:552:3: warning: ISO C90 forbids mixed declarations and code [-Wpedantic]
   int xx,yy;
   ^
Fix -Wunused-variable compiler warning.

In particular:
wmx11pixmap.c: In function ‘RGBtoXIm’:
wmx11pixmap.c:34:18: warning: unused variable ‘p8’ [-Wunused-variable]
  unsigned char * p8 = (unsigned char *)ximout->data;
                  ^
Fix -Wunused-result compiler warnings.

In particular:
bubblemon.c: In function ‘main’:
bubblemon.c:447:6: warning: ignoring return value of ‘system’, declared with attribute warn_unused_result [-Wunused-result]
      system(execute);
      ^
sys_linux.c: In function ‘system_cpu’:
sys_linux.c:38:2: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result]
  fscanf(stat, "%*s %"PRIu64" %"PRIu64" %"PRIu64" %"PRIu64,
  ^
sys_linux.c: In function ‘system_memory’:
sys_linux.c:84:2: warning: ignoring return value of ‘fread’, declared with attribute warn_unused_result [-Wunused-result]
  fread(shit, 2048, 1, mem);
  ^
sys_linux.c: In function ‘system_loadavg’:
sys_linux.c:115:2: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result]
  fscanf(avg, "%d.%d %d.%d %d.%d", &bm.loadavg[0].i, &bm.loadavg[0].f,
  ^
Further FreeBSD updates.

Remove the dependency on libkvm and the need for a setgid binary by using
sysctl to determine memory and swap usage.

Based on similar patches for wmmemload.  See:
http://repo.or.cz/w/dockapps.git/commitdiff/a473280ab9850b93ba2da950cb549c62a2225351?hp=ba72863015547316aaed5e9c42fd179faeeaa911
http://sources.debian.net/src/wmmemload/0.1.7-2/debian/patches/sysctl_swap.patch/