autotools m4 breakage from v2.0.12 to v2.0.13

m4 package finding is breaking between the versions v2.0.12 to v2.0.13

If I build the package sox, the m4 code works for the earlier version and then breaks for the latter.
At the end of configure, for v2.0.12 I get : oggvorbis..................yes
At the end of configure, for v2.0.13 I get : oggvorbis..................no

To reproduce .... put the script at the end of this issue in the file /tmp/wasmBreakage.sh

I install/actiave v2.0.12 and remove build directories and then rebuild :
```
./emsdk install 2.0.12
./emsdk activate 2.0.12
# create a new terminal to get rid of residual env vars.
rm -rf /tmp/wasm; /tmp/wasmBreakage.sh
```
At the end of the execution, I see : oggvorbis..................yes

I install/actiave 2.0.13 and remove build directories and then rebuild :
```
./emsdk install 2.0.13
./emsdk activate 2.0.13
# create a new terminal to get rid of residual env vars.
rm -rf /tmp/wasm; /tmp/wasmBreakage.sh
```
At the end of the execution, I see : oggvorbis..................no

```
#########################################################################################
# File : wasmBreakage.sh
# Author Matt Flax
# Date 20210324
# Demonstrates m4 breakage with emscripten

source /usr/local/emsdk/emsdk_env.sh

export BUILD_DIR=/tmp/wasm
export EMSCRIPTEN=$EMSDK/upstream/emscripten/system

if [ ! -d $BUILD_DIR ]; then
mkdir $BUILD_DIR

cd $BUILD_DIR

OGG_DIR=libogg-1.3.4
wget https://ftp.osuosl.org/pub/xiph/releases/ogg/$OGG_DIR.tar.gz
tar zxpvf $OGG_DIR.tar.gz
cd $OGG_DIR
emconfigure ./configure --enable-shared --prefix=$EMSCRIPTEN
emmake make -j8
emmake make install

cd $BUILD_DIR

VORBIS_DIR=libvorbis-1.3.6
wget https://ftp.osuosl.org/pub/xiph/releases/vorbis/$VORBIS_DIR.tar.gz
tar zxpvf $VORBIS_DIR.tar.gz
cd $VORBIS_DIR
./autogen.sh
emconfigure ./configure --enable-shared --prefix=$EMSCRIPTEN
emmake make -j8
emmake make install

cd $BUILD_DIR

export SOX_DIR=sox-git
git clone --depth=1 git://git.code.sf.net/u/flatmax/sox $SOX_DIR
cd $SOX_DIR
autoreconf -i
emconfigure ./configure --enable-shared --prefix=$EMSCRIPTEN
else
echo ERROR $BUILD_DIR should be rm before running
fi
############################################################################################
```
[wasmBreakage.txt](https://github.com/emscripten-core/emscripten/files/6194609/wasmBreakage.txt)