leveldb: generate pic for static libraries

leveldb: generate pic for static libraries

The project's static libraries are not compiled with the -fPIC compiler
flag. This prevents dynamic libraries to link against those libraries.

This commit adds a patch that sets the -fPIC compiler flag to the list of
CFLAGS/CXXFLAGS.

The project now generates position independant code for all of its
outputs (i.e. not limited anymore to its shared libraries).

Fixes:

	/home/gportay/src/buildroot/output/host/opt/ext-toolchain/bin/../lib/gcc/x86_64-amd-linux-gnu/6.2.0/../../../../x86_64-amd-linux-gnu/bin/ld: /home/gportay/src/buildroot/output/host/x86_64-buildroot-linux-gnu/sysroot/usr/lib/libmemenv.a(memenv.o): relocation R_X86_64_32S against `.rodata' can not be used when making a shared object; recompile with -fPIC
	/home/gportay/src/buildroot/output/host/x86_64-buildroot-linux-gnu/sysroot/usr/lib/libmemenv.a: error adding symbols: Bad value
	collect2: error: ld returned 1 exit status

Signed-off-by: Gaël PORTAY <gael.portay@collabora.com>
[Arnout: renumber patch]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>