Index: Makefile.in
===================================================================
--- Makefile.in	(revision 89791)
+++ Makefile.in	(working copy)
@@ -87,6 +87,9 @@
 BUILTIN_TRANSOBJS = @BUILTIN_TRANSOBJS@
 POSTLINK = @POSTLINK@
 
+PKG_CONFIG = @PKG_CONFIG@
+PKG_CONFIG_PATH = @PKG_CONFIG_PATH@
+
 RUBY_BASE_NAME=@RUBY_BASE_NAME@
 RUBY_PROGRAM_VERSION=@RUBY_PROGRAM_VERSION@
 RUBY_INSTALL_NAME=@RUBY_INSTALL_NAME@
Index: common.mk
===================================================================
--- common.mk	(revision 89791)
+++ common.mk	(working copy)
@@ -181,7 +181,8 @@
 EXTS_MK = exts.mk
 $(EXTS_MK): $(MKFILES) all-incs $(PREP) $(RBCONFIG) $(LIBRUBY)
 	$(ECHO) generating makefile $@
-	$(Q)$(MINIRUBY) $(srcdir)/ext/extmk.rb --make="$(MAKE)" --command-output=$(EXTS_MK) $(EXTMK_ARGS) configure
+	$(Q) PKG_CONFIG_PATH=$(PKG_CONFIG_PATH) \
+	$(MINIRUBY) $(srcdir)/ext/extmk.rb --make="$(MAKE)" --command-output=$(EXTS_MK) $(EXTMK_ARGS) configure
 
 configure-ext: $(EXTS_MK)
 
diff -ur ../ruby-2.3.8.org/configure ./configure
--- ../ruby-2.3.8.org/configure	2018-10-18 00:37:54.000000000 +0900
+++ ./configure	2021-11-09 19:26:19.000000000 +0900
@@ -773,6 +773,7 @@
 CP
 RM
 PKG_CONFIG
+PKG_CONFIG_PATH
 PYTHON
 DOXYGEN
 DOT
@@ -953,7 +954,8 @@
 CXX
 CXXFLAGS
 CCC
-CPP'
+CPP
+PKG_CONFIG_PATH'
 
 
 # Initialize some variables set by options.
