Alpine 3.6: Unary operator expected (apcu-4.0.11)

[mblaschke]

On alpine 3.6 with PHP 5.6.30 (in docker image) APCu cannot be build via pecl:

> pecl install apcu-4.0.11
downloading apcu-4.0.11.tar ...
Starting to download apcu-4.0.11.tar (779,264 bytes)
.............................................done: 779,264 bytes
43 source files, building
running: phpize5
Configuring for:
PHP Api Version:         20131106
Zend Module Api No:      20131226
Zend Extension Api No:   220131226
Enable full APC compatibility [yes] :
Enable internal debugging in APCu [no] :
building in /tmp/pear/temp/pear-build-defaultusernBACLM/apcu-4.0.11
running: /tmp/pear/temp/apcu/configure --with-php-config=/usr/bin/php-config5 --enable-apc-bc=yes --enable-apcu-debug=no
checking for grep that handles long lines and -e... /bin/grep
checking for egrep... /bin/grep -E
checking for a sed that does not truncate output... /bin/sed
expr: syntax error
/tmp/pear/temp/apcu/configure: line 2532: test: =: unary operator expected
expr: syntax error
/tmp/pear/temp/apcu/configure: line 2538: test: =: unary operator expected
expr: syntax error
/tmp/pear/temp/apcu/configure: line 2545: test: =: unary operator expected
expr: syntax error
/tmp/pear/temp/apcu/configure: line 2538: test: =: unary operator expected
expr: syntax error
/tmp/pear/temp/apcu/configure: line 2545: test: =: unary operator expected
expr: syntax error
/tmp/pear/temp/apcu/configure: line 2538: test: =: unary operator expected
expr: syntax error
/tmp/pear/temp/apcu/configure: line 2545: test: =: unary operator expected
checking for cc... cc
checking whether the C compiler works... no
configure: error: in `/tmp/pear/temp/pear-build-defaultusernBACLM/apcu-4.0.11':
configure: error: C compiler cannot create executables
See `config.log' for more details
ERROR: `/tmp/pear/temp/apcu/configure --with-php-config=/usr/bin/php-config5 --enable-apc-bc=yes --enable-apcu-debug=no' failed

Maybe related to php/php-src@660250f