https://cgit.freebsd.org/ports/tree/devel/wasi-libc/Makefile#n40
avoid rebuilding everything in fake

wasi-libc requires some compiler headers that we remove from our
llvm ports so we include them here instead

Index: Makefile
--- Makefile.orig
+++ Makefile
@@ -224,7 +224,7 @@ endif
 #    should come earlier in the search path, so they can "override"
 #    and/or `#include_next` the public headers. `-isystem` (like
 #    `-idirafter`) comes later in the search path than `-I`.
-CFLAGS += -isystem "$(SYSROOT_INC)"
+CFLAGS += -isystem "$(SYSROOT_INC)" -isystem "${WRKDIR}/sysroot/include"
 
 # These variables describe the locations of various files and directories in
 # the build tree.
@@ -565,7 +565,7 @@ check-symbols: startup_files libc
 	# This ignores whitespace because on Windows the output has CRLF line endings.
 	diff -wur "$(CURDIR)/expected/$(MULTIARCH_TRIPLE)" "$(SYSROOT_SHARE)"
 
-install: finish
+install:
 	mkdir -p "$(INSTALL_DIR)"
 	cp -r "$(SYSROOT)/lib" "$(SYSROOT)/share" "$(SYSROOT)/include" "$(INSTALL_DIR)"