vm/master.hpp: optional reproducible VM compilation

The old behaviour of building with `__DATE__` and
    `__TIME__` is still the default, but now it's
    possible to use `-DREPRODUCIBLE=1` and the
    `REPRODUCIBLE=1` parameter to `make` and `nmake`.

Specifically, this replaces the value of
    `FACTOR_COMPILE_TIME` with the string constant
    `"[reproducible]"`. This is purely a cosmetic
    change.

GNUmakefile

@@ -1,6 +1,7 @@
 ifdef CONFIG
 	VERSION = 0.99
 	GIT_LABEL = $(shell echo `git describe --all`-`git rev-parse HEAD`)
+	REPRODUCIBLE ?= 0
 
 	BUNDLE = Factor.app
 
@@ -10,6 +11,7 @@ ifdef CONFIG
 		-pedantic \
 		-DFACTOR_VERSION="$(VERSION)" \
 		-DFACTOR_GIT_LABEL="$(GIT_LABEL)" \
+		-DFACTOR_REPRODUCIBLE="$(REPRODUCIBLE)" \
 		$(SITE_CFLAGS)
 
 	CXXFLAGS += -std=c++11

Nmakefile

@@ -65,6 +65,10 @@ LINK_FLAGS = $(LINK_FLAGS) /DEBUG
 CL_FLAGS = $(CL_FLAGS) /Zi /DFACTOR_DEBUG
 !ENDIF
 
+!IF DEFINED(REPRODUCIBLE)
+CL_FLAGS = $(CL_FLAGS) /DFACTOR_REPRODUCIBLE=1
+!ENDIF
+
 ML_FLAGS = /nologo /safeseh
 
 EXE_OBJS = vm\main-windows.obj vm\factor.res

vm/master.hpp

@@ -52,8 +52,13 @@
 #define FACTOR_COMPILER_VERSION "unknown"
 #endif
 
+#if (FACTOR_REPRODUCIBLE == 1)
+  #pragma message "REPRODUCIBLE"
+  #define FACTOR_COMPILE_TIME "[reproducible]"
+#else
   // Record compilation time
   #define FACTOR_COMPILE_TIME  __DATE__ " " __TIME__
+#endif
 
 // Detect target CPU type
 #if defined(__arm__)