Make GIT_HASH work when one uses a separate build directory.

My previous definition of GIT_HASH only worked when one built Csmith
in the source tree.  The new definition works when one builds in a
separate directory, too.
(cherry picked from commit ddbef56)

runtime/Makefile.am

@@ -39,7 +39,7 @@ lib_LIBRARIES = libcsmith.a
 libcsmith_a_SOURCES = \
 	volatile_runtime.c
 
-GIT_HASH := $(shell git show -s --format=%h . 2>/dev/null || echo exported)
+GIT_HASH := $(shell (cd "$(top_srcdir)" && git show -s --format=%h . 2>/dev/null) || echo exported)
 GIT_FLAG = -DGIT_VERSION=\"$(GIT_HASH)\"
 
 ## ENE: The idea of stuffing the target CPU name (a string) into a CPP symbol

runtime/Makefile.in

@@ -204,7 +204,7 @@ lib_LIBRARIES = libcsmith.a
 libcsmith_a_SOURCES = \
 	volatile_runtime.c
 
-GIT_HASH := $(shell git show -s --format=%h . 2>/dev/null || echo exported)
+GIT_HASH := $(shell (cd "$(top_srcdir)" && git show -s --format=%h . 2>/dev/null) || echo exported)
 GIT_FLAG = -DGIT_VERSION=\"$(GIT_HASH)\"
 libcsmith_a_CPPFLAGS = \
 	-DTARGET_CPU_$(target_cpu)=1 \

src/Makefile.am

@@ -191,7 +191,7 @@ EXTRA_DIST = \
 	csmith.vcproj \
 	csmith.vcxproj
 
-GIT_HASH := $(shell git show -s --format=%h . 2>/dev/null || echo exported)
+GIT_HASH := $(shell (cd "$(top_srcdir)" && git show -s --format=%h . 2>/dev/null) || echo exported)
 GIT_FLAG = -DGIT_VERSION=\"$(GIT_HASH)\"
 
 ## ENE: The idea of stuffing the target CPU name (a string) into a CPP symbol

src/Makefile.in

@@ -384,7 +384,7 @@ EXTRA_DIST = \
 	csmith.vcproj \
 	csmith.vcxproj
 
-GIT_HASH := $(shell git show -s --format=%h . 2>/dev/null || echo exported)
+GIT_HASH := $(shell (cd "$(top_srcdir)" && git show -s --format=%h . 2>/dev/null) || echo exported)
 GIT_FLAG = -DGIT_VERSION=\"$(GIT_HASH)\"
 csmith_CPPFLAGS = \
 	-DTARGET_CPU_$(target_cpu)=1 \