version --build-options: also report host CPU

It can be helpful for bug reports to include information about the
environment in which the bug occurs. "git version --build-options" can
help to supplement this information. In addition to the size of 'long'
already reported by --build-options, also report the host's CPU type.
Example output:

   $ git version --build-options
   git version 2.9.3.windows.2.826.g06c0f2f
   cpu: x86_64
   sizeof-long: 4

New Makefile variable HOST_CPU supports cross-compiling.

Suggested-by: Adric Norris <landstander668@gmail.com>
Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: sunshineco

Makefile

@@ -425,6 +425,9 @@ all::
 #
 # to say "export LESS=FRX (and LV=-c) if the environment variable
 # LESS (and LV) is not set, respectively".
+#
+# When cross-compiling, define HOST_CPU as the canonical name of the CPU on
+# which the built Git will run (for instance "x86_64").
 
 GIT-VERSION-FILE: FORCE
 	@$(SHELL_PATH) ./GIT-VERSION-GEN
@@ -1095,6 +1098,12 @@ else
 BROKEN_PATH_FIX = '/^\# @@BROKEN_PATH_FIX@@$$/d'
 endif
 
+ifeq (,$(HOST_CPU))
+	BASIC_CFLAGS += -DGIT_HOST_CPU="\"$(firstword $(subst -, ,$(uname_M)))\""
+else
+	BASIC_CFLAGS += -DGIT_HOST_CPU="\"$(HOST_CPU)\""
+endif
+
 ifneq (,$(INLINE))
 	BASIC_CFLAGS += -Dinline=$(INLINE)
 endif

help.c

@@ -412,6 +412,7 @@ int cmd_version(int argc, const char **argv, const char *prefix)
 	printf("git version %s\n", git_version_string);
 
 	if (build_options) {
+		printf("cpu: %s\n", GIT_HOST_CPU);
 		printf("sizeof-long: %d\n", (int)sizeof(long));
 		/* NEEDSWORK: also save and output GIT-BUILD_OPTIONS? */
 	}