From 8efe46dceeaf08984477003d07efd5d80865cde5 Mon Sep 17 00:00:00 2001
From: Bastien Bouclet <bastien.bouclet@gmail.com>
Date: Fri, 16 Nov 2018 18:21:57 +0100
Subject: [PATCH] BUILD: Set PKG_CONFIG_LIBDIR only when needed when running
 configure

Remember if PKG_CONFIG_LIBDIR is set when running configure manually,
when automatically running configure, only set PKG_CONFIG_LIBDIR if it
was set during the manual run.

Fixes #10807.
---
 Makefile  | 28 +++++++++++++++++++---------
 configure |  2 +-
 2 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/Makefile b/Makefile
index bbba24f0921..56ebfc73b52 100644
--- a/Makefile
+++ b/Makefile
@@ -82,20 +82,30 @@ EXECUTABLE  := $(EXEPRE)scummvm$(EXEEXT)
 
 include $(srcdir)/Makefile.common
 
-# check if configure has been run or has been changed since last run
 ENGINE_SUBDIRS_CONFIGURE := $(wildcard $(srcdir)/engines/*/configure.engine)
+
+config.h:
+SAVED_ENV_VARS = AR AS ASFLAGS CPPFLAGS CXX CXXFLAGS LD LDFLAGS RANLIB SDL_CONFIG STRIP WINDRES WINDRESFLAGS
+
+# The environment variable PKG_CONFIG_LIBDIR has a different meaning
+# for pkg-config when it is empty and when it is not defined.
+# When PKG_CONFIG_LIBDIR is defined but empty, the .pc files cannot
+# be found because the search path is empty.
+# Here we make sure not to define PKG_CONFIG_LIBDIR when automatically
+# running configure and it was not set for the previous run
+# so pkg-config uses the system default search path for the .pc files.
+ifneq ($(SAVED_PKG_CONFIG_LIBDIR),unset)
+	SAVED_ENV_VARS += PKG_CONFIG_LIBDIR
+endif
+
+# check if configure has been run or has been changed since last run
 config.h: $(srcdir)/configure $(ENGINE_SUBDIRS_CONFIGURE)
 ifeq "$(findstring config.mk,$(MAKEFILE_LIST))" "config.mk"
 	@echo "Running $(srcdir)/configure with the last specified parameters"
 	@sleep 2
-	AR="$(SAVED_AR)" AS="$(SAVED_AS)" ASFLAGS="$(SAVED_ASFLAGS)" \
-		CPPFLAGS="$(SAVED_CPPFLAGS)" CXX="$(SAVED_CXX)" \
-		CXXFLAGS="$(SAVED_CXXFLAGS)" LD="$(SAVED_LD)" \
-		LDFLAGS="$(SAVED_LDFLAGS)" PKG_CONFIG_LIBDIR="$(SAVED_PKG_CONFIG_LIBDIR)" \
-		RANLIB="$(SAVED_RANLIB)" SDL_CONFIG="$(SAVED_SDL_CONFIG)" \
-		STRIP="$(SAVED_STRIP)" WINDRES="$(SAVED_WINDRES)" \
-		WINDRESFLAGS="$(SAVED_WINDRESFLAGS)" \
-			$(srcdir)/configure $(SAVED_CONFIGFLAGS)
+
+	$(foreach VAR,$(SAVED_ENV_VARS),$(VAR)="$(SAVED_$(VAR))") \
+		$(srcdir)/configure $(SAVED_CONFIGFLAGS)
 else
 	$(error You need to run $(srcdir)/configure before you can run make. Check $(srcdir)/configure --help for a list of parameters)
 endif
diff --git a/configure b/configure
index 161551e616e..1d050f03a69 100755
--- a/configure
+++ b/configure
@@ -38,7 +38,7 @@ SAVED_CXXFLAGS=$CXXFLAGS
 SAVED_DWP=$DWP
 SAVED_LD=$LD
 SAVED_LDFLAGS=$LDFLAGS
-SAVED_PKG_CONFIG_LIBDIR=$PKG_CONFIG_LIBDIR
+SAVED_PKG_CONFIG_LIBDIR=${PKG_CONFIG_LIBDIR:-unset}
 SAVED_RANLIB=$RANLIB
 SAVED_SDL_CONFIG=$SDL_CONFIG
 SAVED_STRIP=$STRIP