fix(main/guile): fully implement 32-bit hostbuild

- Fixes multiple malformations in the 32-bit builds of `guile` 3.0.10, including but not limited to this MRE of a `WARNING`:

```
~ $ cat hello.scm
!#
(display "Hello, world!")
(newline)
~ $ ./hello.scm
;;; WARNING: compilation of /data/data/com.termux/files/home/./hello.scm failed:
;;; In procedure load-thunk-from-memory: ELF file does not have native word size
Hello, world!
~ $
```

- Necessary after these three upstream Guile commits and other commits which depend on them:
  - https://cgit.git.savannah.gnu.org/cgit/guile.git/commit/?id=137b0e85b956a7b7e7c9bc0029d09fe6868e5b17
  - https://cgit.git.savannah.gnu.org/cgit/guile.git/commit/?id=c758c99b5e37408e48dc1b22c73d6ec35d9de866
  - https://cgit.git.savannah.gnu.org/cgit/guile.git/commit/?id=88e0933450ed9f1cc96858641e0756ffa44c53c6

- Tangentially related follow-up to https://github.com/termux/termux-packages/pull/26977, but **that PR is still necessary also, this PR does not replace it**.

- Necessary to complete https://github.com/termux/termux-packages/pull/25962

packages/guile/build.sh

@@ -3,7 +3,10 @@ TERMUX_PKG_DESCRIPTION="Portable, embeddable Scheme implementation written in C"
 TERMUX_PKG_LICENSE="LGPL-3.0"
 TERMUX_PKG_MAINTAINER="@termux"
 TERMUX_PKG_VERSION=3.0.10
-TERMUX_PKG_REVISION=1
+TERMUX_PKG_REVISION=2
+# Tip: Guile official source code contains hardlinks and cannot be built by default if "$TERMUX_ON_DEVICE_BUILD" == "true".
+# To build if "$TERMUX_ON_DEVICE_BUILD" == "true", follow a guide like this to prepare for it:
+# https://unix.stackexchange.com/questions/265024/unpacking-tarball-with-hard-links-on-a-file-system-that-doesnt-support-hard-lin
 TERMUX_PKG_SRCURL=https://mirrors.kernel.org/gnu/guile/guile-$TERMUX_PKG_VERSION.tar.gz
 TERMUX_PKG_SHA256=2dbdbc97598b2faf31013564efb48e4fed44131d28e996c26abe8a5b23b56c2a
 TERMUX_PKG_DEPENDS="libandroid-spawn, libandroid-support, libffi, libgc, libgmp, libiconv, libunistring, ncurses, readline"
@@ -28,24 +31,116 @@ ac_cv_func_GC_move_disappearing_link=yes
 ac_cv_func_GC_is_heap_ptr=yes
 "
 
-termux_step_host_build() {
-	mkdir HOSTBUILDINSTALL
+_load_ubuntu_packages() {
+	export HOSTBUILD_ROOTFS="${TERMUX_PKG_HOSTBUILD_DIR}/ubuntu_packages"
+	if [[ "$TERMUX_ARCH_BITS" == "32" ]]; then
+		export HOSTBUILD_ARCH="i386"
+		export HOSTBUILD_ARCH_LIBDIR="/usr/lib/i386-linux-gnu"
+		export HOSTBUILD_ARCH_INCLUDEDIR="/usr/include/i386-linux-gnu"
+	else
+		export HOSTBUILD_ARCH="amd64"
+		export HOSTBUILD_ARCH_LIBDIR="/usr/lib/x86_64-linux-gnu"
+		export HOSTBUILD_ARCH_INCLUDEDIR="/usr/include/x86_64-linux-gnu"
+	fi
+	export LD_LIBRARY_PATH="${HOSTBUILD_ROOTFS}${HOSTBUILD_ARCH_LIBDIR}"
+	LD_LIBRARY_PATH+=":${HOSTBUILD_ROOTFS}/usr/lib"
+}
 
-	../src/configure --prefix=$TERMUX_PKG_HOSTBUILD_DIR/HOSTBUILDINSTALL # CFLAGS="-m32" LDFLAGS=" -L/usr/lib/i386-linux-gnu" --host=i386-linux-gnu
-	make -j $TERMUX_PKG_MAKE_PROCESSES
+# Function to obtain the .deb URL
+obtain_deb_url() {
+	local url attempt retries wait PAGE deb_url
+	url="https://packages.ubuntu.com/noble/$HOSTBUILD_ARCH/$1/download"
+	retries=50
+	wait=50
+	>&2 echo "url: $url"
+	for ((attempt=1; attempt<=retries; attempt++)); do
+		PAGE="$(curl -s "$url")"
+		deb_url="$(grep -oE 'https?://.*\.deb' <<< "$PAGE" | head -n1)"
+		if [[ -n "$deb_url" ]]; then
+				echo "$deb_url"
+				return 0
+		else
+			>&2 echo "Attempt $attempt: Failed to obtain deb URL. Retrying in $wait seconds..."
+		fi
+		sleep "$wait"
+	done
+	termux_error_exit "Failed to obtain URL after $retries attempts."
+}
+
+_install_ubuntu_packages() {
+	# install Ubuntu packages, like in the aosp-libs build.sh
+	export HOSTBUILD_ROOTFS="${TERMUX_PKG_HOSTBUILD_DIR}/ubuntu_packages"
+	mkdir -p "${HOSTBUILD_ROOTFS}"
+	local URL DEB_NAME DEB_LIST
+	DEB_LIST="$@"
+	for i in $DEB_LIST; do
+		echo "deb: $i"
+		URL="$(obtain_deb_url "$i")"
+		DEB_NAME="${URL##*/}"
+		termux_download "$URL" "${TERMUX_PKG_CACHEDIR}/${DEB_NAME}" SKIP_CHECKSUM
+		mkdir -p "${TERMUX_PKG_TMPDIR}/${DEB_NAME}"
+		ar x "${TERMUX_PKG_CACHEDIR}/${DEB_NAME}" --output="${TERMUX_PKG_TMPDIR}/${DEB_NAME}"
+		tar xf "${TERMUX_PKG_TMPDIR}/${DEB_NAME}"/data.tar.* \
+			-C "${HOSTBUILD_ROOTFS}"
+	done
+	find "${HOSTBUILD_ROOTFS}" -type f -name '*.pc' | \
+		xargs -n 1 sed -i -e "s|/usr|${HOSTBUILD_ROOTFS}/usr|g"
+}
+
+termux_step_host_build() {
+	if [[ "$TERMUX_ON_DEVICE_BUILD" == "true" ]]; then
+		return
+	fi
+
+	_load_ubuntu_packages
+	_install_ubuntu_packages libffi8 \
+							libffi-dev \
+							libgc1 \
+							libgc-dev \
+							libgmp10 \
+							libgmp-dev \
+							libreadline8t64 \
+							libreadline-dev \
+							libgpm2 \
+							libtinfo6 \
+							libncurses6 \
+							libncursesw6 \
+							libncurses-dev \
+							libunistring5 \
+							libunistring-dev
+
+	export CFLAGS="-I${HOSTBUILD_ARCH_INCLUDEDIR} -I${HOSTBUILD_ROOTFS}${HOSTBUILD_ARCH_INCLUDEDIR}"
+	export LDFLAGS="-L${HOSTBUILD_ARCH_LIBDIR} -L${HOSTBUILD_ROOTFS}${HOSTBUILD_ARCH_LIBDIR}"
+
+	local HOSTBUILD_EXTRA_CONFIGURE_ARGS_32=""
+	if [[ "$TERMUX_ARCH_BITS" == "32" ]]; then
+		export CFLAGS+=" -m32"
+		HOSTBUILD_EXTRA_CONFIGURE_ARGS_32="--host=i386-linux-gnu"
+	fi
+
+	../src/configure --prefix="$HOSTBUILD_ROOTFS/usr" $HOSTBUILD_EXTRA_CONFIGURE_ARGS_32
+	make -j "$TERMUX_PKG_MAKE_PROCESSES"
 	make install
 }
 
 termux_step_pre_configure() {
-	export GUILE_FOR_BUILD="$TERMUX_PKG_HOSTBUILD_DIR"/HOSTBUILDINSTALL/bin/guile
-	export LD_LIBRARY_PATH="$TERMUX_PKG_HOSTBUILD_DIR"/HOSTBUILDINSTALL/lib
-
-	export CC_FOR_BUILD="gcc -m${TERMUX_ARCH_BITS}"
-
 	# Value of PKG_CONFIG becomes hardcoded in bin/*-config
 	export PKG_CONFIG=pkg-config
+
+	if [[ "$TERMUX_ON_DEVICE_BUILD" == "true" ]]; then
+		return
+	fi
+
+	# always remove this because the hostbuild may be for a different architecture
+	rm -rf "$TERMUX_HOSTBUILD_MARKER"
+
+	_load_ubuntu_packages
+
+	export GUILE_FOR_BUILD="$HOSTBUILD_ROOTFS/usr/bin/guile"
+
+	export CC_FOR_BUILD="gcc -m${TERMUX_ARCH_BITS}"
 }
 
 termux_step_post_configure() {
-	cp $TERMUX_PKG_BUILDER_DIR/malloc.h $TERMUX_PKG_BUILDDIR/lib/
+	cp "$TERMUX_PKG_BUILDER_DIR/malloc.h" "$TERMUX_PKG_BUILDDIR/lib/"
 }