Allow env vars (not only command line overrides) to set CPUFEATURES_{ARCH,UNAME}.

Change CPUFEATURES_{ARCH,UNAME} defaults to use {ARCH,UNAME} values.

Fixes #158

Makefile

@@ -39,7 +39,11 @@ else
   LIMESDR ?= no
 endif
 
-UNAME := $(shell uname)
+HOST_UNAME := $(shell uname)
+HOST_ARCH := $(shell uname -m)
+
+UNAME ?= $(HOST_UNAME)
+ARCH ?= $(HOST_ARCH)
 
 ifeq ($(UNAME), Linux)
   CPPFLAGS += -D_DEFAULT_SOURCE
@@ -150,7 +154,6 @@ endif
 ## starch (runtime DSP code selection) mix, architecture-specific
 ##
 
-ARCH ?= $(shell uname -m)
 ifneq ($(CPUFEATURES),yes)
   # need to be able to detect CPU features at runtime to enable any non-standard compiler flags
   STARCH_MIX := generic
@@ -180,6 +183,7 @@ include dsp/generated/makefile.$(STARCH_MIX)
 showconfig:
 	@echo "Building with:" >&2
 	@echo "  Version string:  $(DUMP1090_VERSION)" >&2
+	@echo "  Architecture:    $(ARCH)" >&2
 	@echo "  DSP mix:         $(STARCH_MIX)" >&2
 	@echo "  RTLSDR support:  $(RTLSDR)" >&2
 	@echo "  BladeRF support: $(BLADERF)" >&2

Makefile.cpufeatures

@@ -2,8 +2,8 @@
 
 # cmake integration is a little tricky, so let's do this by hand for now
 
-CPUFEATURES_UNAME := $(shell uname)
-CPUFEATURES_ARCH := $(shell uname -m)
+CPUFEATURES_UNAME ?= $(UNAME)
+CPUFEATURES_ARCH ?= $(ARCH)
 
 CPUFEATURES_OBJS := cpu_features/src/filesystem.o cpu_features/src/stack_line_reader.o cpu_features/src/string_view.o
 CPUFEATURES_CFLAGS := -std=c99 -O -g -DSTACK_LINE_READER_BUFFER_SIZE=1024 -DNDEBUG