external/libecc: Remove -ffreestanding

This causes issues when FreeBSD cross-builds pkg for a different
architecture (e.g., building for powerpc64 from amd64) using a
non-default sysroot:

--- ec_params.pico ---
In file included from /build/obj/bsd/src/bsd/dev/powerpc.powerpc64/tmp/usr/include/inttypes.h:33:
/build/obj/bsd/src/bsd/dev/powerpc.powerpc64/tmp/usr/include/sys/stdint.h:48:24: error: typedef redefinition with different types ('__int_fast8_t' (aka 'int') vs 'int8_t' (aka 'signed char'
))
   48 | typedef __int_fast8_t           int_fast8_t;
      |                                 ^
/pkg/llvm19/lib/clang/19/include/stdint.h:280:24: note: previous definition is here
  280 | typedef __int_least8_t int_fast8_t;
      |                        ^

Author: llfw

external/libecc/Makefile.autosetup

@@ -138,7 +138,6 @@ CONFLICTS=	-Dsha256_init=_libecc_sha256_init \
 LOCAL_CFLAGS=	-I$(top_srcdir)/external/libecc/include \
 		-I$(top_srcdir)/compat \
 		-I$(top_builddir)/ \
-		-ffreestanding \
 		-fno-builtin \
 		-fstack-protector-strong \
 		-DUSE_WARN_UNUSED_RET \