Run "sh ./configure" rather than "sh configure"; part of #7992

This fixes a bug with how configure re-execs itself.

libffi/ghc.mk

@@ -88,7 +88,7 @@ $(libffi_STAMP_CONFIGURE): $(TOUCH_DEP)
 	    NM=$(NM) \
         CFLAGS="$(SRC_CC_OPTS) $(CONF_CC_OPTS_STAGE1) -w" \
         LDFLAGS="$(SRC_LD_OPTS) $(CONF_GCC_LINKER_OPTS_STAGE1) -w" \
-        "$(SHELL)" configure \
+        "$(SHELL)" ./configure \
 	          --prefix=$(TOP)/libffi/build/inst \
 	          --libdir=$(TOP)/libffi/build/inst/lib \
 	          --enable-static=yes \