Install build time deps from docker-php-ext-install for alpine

We don't need the build dependencies during runtime, so we temporarily
install them when building extension. This reduces image size with 50%.

We also provide a PHPIZE_DEPS environment variable with the needed deps.

Dockerfile-alpine.template

@@ -1,16 +1,5 @@
 FROM alpine:3.3
 
-# phpize deps
-RUN apk add --no-cache --virtual .phpize-deps \
-		autoconf \
-		file \
-		g++ \
-		gcc \
-		libc-dev \
-		make \
-		pkgconf \
-		re2c
-
 # persistent / runtime deps
 RUN apk add --no-cache --virtual .persistent-deps \
 		ca-certificates \
@@ -37,8 +26,11 @@ ENV PHP_VERSION %%PHP_VERSION%%
 ENV PHP_FILENAME %%PHP_FILENAME%%
 ENV PHP_SHA256 %%PHP_SHA256%%
 
+ENV PHPIZE_DEPS autoconf file g++ gcc libc-dev make pkgconf re2c
+
 RUN set -xe \
 	&& apk add --no-cache --virtual .build-deps \
+		$PHPIZE_DEPS \
 		curl-dev \
 		gnupg \
 		libedit-dev \

docker-php-ext-install

@@ -55,6 +55,11 @@ if [ -z "$exts" ]; then
 	exit 1
 fi
 
+: ${PHPIZE_DEPS:="autoconf file g++ gcc libc-dev make pkgconf re2c"}
+if [ -e /lib/apk/db/installed ]; then
+	apk add --no-cache --virtual .phpize-deps $PHPIZE_DEPS
+fi
+
 for ext in $exts; do
 	(
 		cd "$ext"
@@ -69,3 +74,7 @@ for ext in $exts; do
 		make -j"$j" clean
 	)
 done
+
+if [ -e /lib/apk/db/installed ]; then
+	apk del .phpize-deps
+fi