build system: use a bit more aggressive gcc/ld optimizations,

build system: use a bit more aggressive gcc/ld optimizations,
mostly related to ELF section ans padding, not code gen.
Resulting reductions in size (only biggest ones are shown)
uClibc.t4 - new, uClibc.t3 - old:

  15673     244      92   16009    3e89 uClibc.t4-stdcfg_so/lib/ld-uClibc-0.9.29.so
  15673     244      92   16009    3e89 uClibc.t4-stdcfg_so/lib/ld-uClibc.so
  15673     244      92   16009    3e89 uClibc.t4-stdcfg_so/lib/ld-uClibc.so.0
  15678     244      92   16014    3e8e uClibc.t3-stdcfg_so/lib/ld-uClibc-0.9.29.so
  15678     244      92   16014    3e8e uClibc.t3-stdcfg_so/lib/ld-uClibc.so
  15678     244      92   16014    3e8e uClibc.t3-stdcfg_so/lib/ld-uClibc.so.0
  39910     200       4   40114    9cb2 uClibc.t4-stdcfg_so/lib/libm-0.9.29.so
  39910     200       4   40114    9cb2 uClibc.t4-stdcfg_so/lib/libm.so
  39910     200       4   40114    9cb2 uClibc.t4-stdcfg_so/lib/libm.so.0
  40179     200       4   40383    9dbf uClibc.t3-stdcfg_so/lib/libm-0.9.29.so
  40179     200       4   40383    9dbf uClibc.t3-stdcfg_so/lib/libm.so
  40179     200       4   40383    9dbf uClibc.t3-stdcfg_so/lib/libm.so.0
 234104    1472    5980  241556   3af94 uClibc.t4-stdcfg_so/lib/libc.so.0
 234104    1472    5980  241556   3af94 uClibc.t4-stdcfg_so/lib/libuClibc-0.9.29.so
 235319    1472    5992  242783   3b45f uClibc.t3-stdcfg_so/lib/libc.so.0
 235319    1472    5992  242783   3b45f uClibc.t3-stdcfg_so/lib/libuClibc-0.9.29.so