Error building Glib due to undefined reference in libffi

I am currently working on building Glib version 2.45.8 on CentOS 7 running on x86-64 targeting a custom distro based off Linux from Scratch running on x86-64. There is a problem linking with libffi which is version 3.2.1.

path/to/build/directory/bin/ld: warning: libc.so.6, needed by //lib/../libffi.so, not found (try using -rpath or -rpath-link)
path/to/build/directory/lib64/libffi.so: undefined reference to `free@GLIBC_2.2.5'
path/to/build/directory/lib64/libffi.so: undefined reference to `mkostemp@GLIBC_2.7'
(etc ... there are about 15 undefined references total)
path/to/build/directory/lib64/libffi.so: undefined reference to `__getdelim@GLIBC_2.2.5'
path/to/build/directory/lib64/libffi.so: undefined reference to `getenv@GLIBC_2.2.5'

Using -rpath or -rpath-link will not work because the libc.so.6 file does not exist anywhere in the file system for my build.

However I do have libc.so and libc.so.0 in path/to/build/directory/lib64/ the directory in which libc.so.6 cannot be found.

Here are my ./configure and make commmands.

glib_cv_stack_grows=no \
glib_cv_uscore=no \
ac_cv_func_posix_getpwuid_r=yes \
ac_cv_func_posix_getgrgid_r=yes \
LIBFFI_CFLAGS=-lffi \
LIBFFI_LIBS=-lffi \
ZLIB_CFLAGS=-lz \
ZLIB_LIBS=-lz \
PKG_CONFIG_LIBDIR=$TARG/lib/pkgconfig \
./configure --prefix=/ --host=x86_64-linux --with-libiconv

make -j32 LDFLAGS=-liconv

How do I get the correct libc.so to be built?