re-add PKG_CONFIG_PATH; more diagnostics

Makefile

@@ -49,6 +49,7 @@ $(foreach arch,$(ARCHS),\
 	$(if $(findstring $(3rdparty_NATIVE_ARCH),$(arch)),,\
 		$(eval _build/$(arch)/%: private export CC=$(arch)-gcc))\
 	$(eval _build/$(arch)/%: private export PKG_CONFIG_LIBDIR=$(CURDIR)/_3rdparty/tgt/$(arch)/lib/pkgconfig)\
+	$(eval _build/$(arch)/%: private export PKG_CONFIG_PATH=$(CURDIR)/_3rdparty/tgt/$(arch)/lib/pkgconfig)\
 	$(eval _build/$(arch)/%: private export GOOS=\
 		$(or $(if $(findstring linux,$(arch)),linux),\
 			 $(if $(findstring mingw,$(arch)),windows),\
@@ -66,9 +67,11 @@ $(if $(findstring x86_64-linux,$(3rdparty_NATIVE_ARCH)),\
 	$(eval unit-test: private export GOOS=linux)\
 	$(eval unit-test: private export GOARCH=amd64)\
 	$(eval unit-test: private export PKG_CONFIG_LIBDIR=$(CURDIR)/_3rdparty/tgt/x86_64-linux-musl/lib/pkgconfig)\
+	$(eval unit-test: private export PKG_CONFIG_PATH=$(CURDIR)/_3rdparty/tgt/x86_64-linux-musl/lib/pkgconfig)\
 	,\
 	$(eval unit-test: private export CC=$(firstword $(shell which gcc cc)))\
-	$(eval unit-test: private export PKG_CONFIG_LIBDIR=$(CURDIR)/_3rdparty/tgt/$(3rdparty_NATIVE_ARCH)/lib/pkgconfig))
+	$(eval unit-test: private export PKG_CONFIG_LIBDIR=$(CURDIR)/_3rdparty/tgt/$(3rdparty_NATIVE_ARCH)/lib/pkgconfig)\
+	$(eval unit-test: private export PKG_CONFIG_PATH=$(CURDIR)/_3rdparty/tgt/$(3rdparty_NATIVE_ARCH)/lib/pkgconfig))
 
 $(EXE) unit-test: private export CGO_ENABLED=1
 $(EXE) unit-test: private export PATH := $(CURDIR)/_3rdparty/tgt/bin:$(PATH)
@@ -110,6 +113,7 @@ $(EXE):
 	$(info [+] GOROOT=$(GOROOT) GOOS=$(GOOS) GOARCH=$(GOARCH) CC=$(CC))
 	$(info [+] PKG_CONFIG_LIBDIR=$(PKG_CONFIG_LIBDIR))
 	$(info [+] PKG_CONFIG_PATH=$(PKG_CONFIG_PATH))
+	which pkg-config
 	pkg-config --list-package-names
 	mkdir -p $(@D)
 	$(GOROOT)/bin/go build \