coreutils: fix build failure for musl

musl doesn't implement re_match and friends and coreutils fails to
detect this properly, so force internal regex routines for musl.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/coreutils/coreutils.mk

@@ -14,7 +14,8 @@ COREUTILS_LICENSE_FILES = COPYING
 COREUTILS_AUTORECONF = YES
 COREUTILS_GETTEXTIZE = YES
 
-COREUTILS_CONF_OPTS = --disable-rpath --enable-single-binary=shebangs
+COREUTILS_CONF_OPTS = --disable-rpath --enable-single-binary=shebangs \
+	$(if $(BR2_TOOLCHAIN_USES_MUSL),--with-included-regex)
 COREUTILS_CONF_ENV = ac_cv_c_restrict=no \
 	ac_cv_func_chown_works=yes \
 	ac_cv_func_euidaccess=no \