Locally built GCC cross-compiler reports MB_LEN_MAX wrong with -D_FORTIFY_SOURCE=2

I am currently building a cross-compiler targeting the PowerPC architecture. It is capable of building Linux binaries that work and can execute on the target, however I hit a problem when I enable the compiler flag "-D_FORTIFY_SOURCE=2". I build a simple hello world application as so:

#include <limits.h>
#include <stdlib.h>

int main(int argc, char* argv[])
{
  return 0;
}

I compile this using my cross-compiler and get the following error:

$ powerpc-linux-gnu-gcc -D_FORTIFY_SOURCE=2 -O2 hello.c
In file included from /opt/crossgcc/powerpc-linux-gnu/include/stdlib.h:958:0,
                 from hello.c:2:
/opt/crossgcc/powerpc-linux-gnu/include/bits/stdlib.h: In function 'wctomb':
/opt/crossgcc/powerpc-linux-gnu/include/bits/stdlib.h:90:3: error: #error "Assumed value of MB_LEN_MAX wrong"
 # error "Assumed value of MB_LEN_MAX wrong"
   ^

I believe this is because I am not bootstrapping my GCC build correctly, but as far as I can see I am building it correctly. The script I am taking to build my compiler are as follows:

#! /bin/bash
set -e
INSTALL_PATH=$PWD/output
TARGET=powerpc-linux-gnu
LINUX_ARCH=powerpc
PARALLEL_MAKE=-j4
BINUTILS_VERSION=binutils-2.32
GCC_VERSION=gcc-8.3.0
LINUX_KERNEL_VERSION=linux-5.1.9
GLIBC_VERSION=glibc-2.29
export PATH=$INSTALL_PATH/bin:$PATH

cd $GCC_VERSION
./contrib/download_prerequisites
cd ..

mkdir -p build-binutils
cd build-binutils
../$BINUTILS_VERSION/configure --prefix=$INSTALL_PATH --target=$TARGET
make $PARALLEL_MAKE
make install
cd ..

cd $LINUX_KERNEL_VERSION
make ARCH=$LINUX_ARCH INSTALL_HDR_PATH=$INSTALL_PATH/$TARGET headers_install
cd ..

# Build GCC compiler
mkdir -p build-gcc
cd build-gcc
../$GCC_VERSION/configure \
  --prefix=$INSTALL_PATH \
  --target=$TARGET \
  --disable-silent-rules \
  --with-gnu-as --with-gnu-ld \
  --enable-languages="c,c++" \
  --enable-theads=posix \
  --enable-c99 \
  --enable-long-long \
  --enable-lto \
  --enable-libssp \
  --enable-secureplt \
  --disable-libmudflag \
  --enable-secureplt \
  --disable-nls \
  --with-long-double-128
make $PARALLEL_MAKE all-gcc
make install-gcc
cd ..

mkdir -p build-glibc
cd build-glibc
../$GLIBC_VERSION/configure \
  --prefix=$INSTALL_PATH/$TARGET \
  --build=$(gcc -dumpmachine) \
  --host=$TARGET \
  --target=$TARGET \
  --with-headers=$INSTALL_PATH/$TARGET/include \
  libc_cv_forced_unwind=yes
make install-bootstrap-headers=yes install-headers
make $PARALLEL_MAKE csu/subdir_lib
install csu/crt1.o csu/crti.o csu/crtn.o $INSTALL_PATH/$TARGET/lib
$TARGET-gcc -nostdlib -nostartfiles -shared -x c /dev/null -o $INSTALL_PATH/$TARGET/lib/libc.so
touch $INSTALL_PATH/$TARGET/include/gnu/stubs.h
cd ..

cd build-gcc
make $PARALLEL_MAKE all-target-libgcc
make install-target-libgcc
cd ..

cd build-glibc
make $PARALLEL_MAKE
make install
cd ..

cd build-gcc
make $PARALLEL_MAKE all
make install
cd ..

Am I incorrectly bootstrapping my GCC? Should I be doing something differently to make GCC "aware" of my glibc headers?