build: make sure asm gets built with -DPIC

Fixes issue openwrt/packages#14921, whereby inline ASM wasn't getting
built as PIC; look at gmp-6.2.1/mpn/x86/pentium/popcount.asm for
example:

ifdef(`PIC',`
...

for a routine that exists in both PIC and non-PIC versions.

Make sure that wherever $(FPIC) gets passed as a variable expansion
that it gets quoted where necessary (such as setting environment
variables in shell commands).

Signed-off-by: Philip Prindeville <philipp@redfish-solutions.com>

rules.mk

@@ -75,12 +75,12 @@ IS_PACKAGE_BUILD := $(if $(filter package/%,$(BUILD_SUBDIR)),1)
 OPTIMIZE_FOR_CPU=$(subst i386,i486,$(ARCH))
 
 ifneq (,$(findstring $(ARCH) , aarch64 aarch64_be powerpc ))
-  FPIC:=-fPIC
+  FPIC:=-DPIC -fPIC
 else
-  FPIC:=-fpic
+  FPIC:=-DPIC -fpic
 endif
 
-HOST_FPIC:=-fPIC
+HOST_FPIC:=-DPIC -fPIC
 
 ARCH_SUFFIX:=$(call qstrip,$(CONFIG_CPU_TYPE))
 GCC_ARCH:=