openswan: do not use -fPIE for static builds

-fPIE produces shared objects, and shared objects need "/lib/ld.so"
which won't be present on a statically built target. So, building
openswan with -static -fPIE is invalid and will fail with an error like
this one:

/br/output/host/opt/ext-toolchain/bin/../lib/gcc/mipsel-ctng-linux-uclibc/4.8.2/../../../../mipsel-ctng-linux-uclibc/bin/ld:
/br/output/host/usr/mipsel-buildroot-linux-uclibc/sysroot/usr/lib/libgmp.a(lt2-add.o):
relocation R_MIPS_HI16 against `__gnu_local_gp' can not be used when
making a shared object; recompile with -fPIC

Fixes:

  http://autobuild.buildroot.net/results/68b/68b2211cc7acfbdfed8d4b161cbdaf1429315017/



Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>