Do build config checks instead of crashing

configure/CONFIG

@@ -2,6 +2,10 @@
 #
 # Do not make changes to this file!
 
+ifeq ($(strip $(EPICS_HOST_ARCH)),)
+  $(warning EPICS_HOST_ARCH is not set.)
+endif
+
 # Allow user to override where the build rules come from
 RULES = $(EPICS_BASE)
 
@@ -13,6 +17,16 @@ ifdef T_A
 -include $(TOP)/configure/RELEASE.$(EPICS_HOST_ARCH).$(T_A)
 endif
 
+ifeq ($(strip $(RULES)),)
+  ifeq ($(strip $(EPICS_BASE)),)
+    $(warning Build error: EPICS_BASE not set after including RELEASE files.)
+  else
+    $(warning Build error: EPICS_BASE set but RULES variable empty.)
+  endif
+  $(error Makefiles loaded: $(MAKEFILE_LIST))
+  # Die before the include of $(CONFIG)/CONFIG below does
+endif
+
 BUILDING_LIBCOM = DEFINED
 
 CONFIG = $(RULES)/configure