Use bash(1) for configure; the script contains lots of bashisms for variable

expension.
This fixes the build where fmin(3) is not a compiler builtin.

reported by sthen@

devel/libplist/Makefile

@@ -2,6 +2,7 @@ COMMENT =		library to handle Apple Property List files
 
 V=			2.2.0
 DISTNAME =		libplist-${V}
+REVISION =		0
 
 SHARED_LIBS +=  plist-2.0            0.0      # 6.0
 SHARED_LIBS +=  plist++-2.0          0.0      # 6.0
@@ -20,6 +21,10 @@ WANTLIB += ${COMPILER_LIBCXX} c m
 
 COMPILER =		base-clang ports-gcc
 
+# lots of bashisms for variable expension (FLAGS += -lfoo)
+CONFIGURE_SCRIPT =	${LOCALBASE}/bin/bash configure
+BUILD_DEPENDS +=	shells/bash
+
 CONFIGURE_STYLE =	gnu
 CONFIGURE_ENV =		LDFLAGS="-L${LOCALBASE}/lib"
 CONFIGURE_ARGS =	--without-cython