macos: use more portable pwd instead of PWD

In nixpkgs we use coreutils and do not have PWD available.
This change have any downsides on normal macOS systems, but helps
nixpkgs packaging a bit.

Signed-off-by: Jörg Thalheim <[email protected]>

make-mac.mk

@@ -1,8 +1,8 @@
 CC=clang
 CXX=clang++
-TOPDIR=$(shell PWD)
+TOPDIR=$(shell pwd)
 
-INCLUDES=-I$(shell PWD)/rustybits/target -isystem $(TOPDIR)/ext  -I$(TOPDIR)/ext/prometheus-cpp-lite-1.0/core/include -I$(TOPDIR)/ext-prometheus-cpp-lite-1.0/3rdparty/http-client-lite/include -I$(TOPDIR)/ext/prometheus-cpp-lite-1.0/simpleapi/include
+INCLUDES=-I$(shell pwd)/rustybits/target -isystem $(TOPDIR)/ext  -I$(TOPDIR)/ext/prometheus-cpp-lite-1.0/core/include -I$(TOPDIR)/ext-prometheus-cpp-lite-1.0/3rdparty/http-client-lite/include -I$(TOPDIR)/ext/prometheus-cpp-lite-1.0/simpleapi/include
 DEFS=
 LIBS=
 ARCH_FLAGS=-arch x86_64 -arch arm64