dmalloc: pass -fPIC when compiling

dmalloc: pass -fPIC when compiling

This is needed to avoid:

/home/test/mips-4.4/bin/mips-linux-gnu-ld --sysroot=/home/test/outputs/test-35/staging -shared --whole-archive -soname libdmallocxx.so -o libdmallocxx.so.t libdmallocxx.a
/home/test/mips-4.4/bin/mips-linux-gnu-ld: libdmalloc.a(arg_check.o): relocation R_MIPS_HI16 against `_dmalloc_flags' can not be used when making a shared object; recompile with -fPIC

It is fixed through a patch to Makefile.in instead of passing a CFLAGS
variable to ./configure environment in order to avoid cluttering the
configuration cache with incorrect values.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>