autoconf: pass -Wall to automake

And fix these warning that appear at autoreconf time:
"`:='-style assignments are not portable"

v2: Fix the recently-converted-to-automake r600.

configure.ac

@@ -16,7 +16,7 @@ AC_INIT([Mesa],[mesa_version],
     [https://bugs.freedesktop.org/enter_bug.cgi?product=Mesa])
 AC_CONFIG_AUX_DIR([bin])
 AC_CANONICAL_HOST
-AM_INIT_AUTOMAKE([foreign])
+AM_INIT_AUTOMAKE([foreign -Wall])
 
 dnl http://people.gnome.org/~walters/docs/build-api.txt
 dnl We don't support srcdir != builddir.

src/gallium/drivers/r300/Makefile.sources

@@ -1,4 +1,4 @@
-C_SOURCES := \
+C_SOURCES = \
 	r300_blit.c \
 	r300_chipset.c \
 	r300_context.c \

src/gallium/drivers/r600/Makefile.sources

@@ -1,4 +1,4 @@
-C_SOURCES := \
+C_SOURCES = \
 	r600_asm.c \
 	r600_blit.c \
 	r600_buffer.c \
@@ -16,4 +16,4 @@ C_SOURCES := \
 	r600_translate.c \
 	r600_state_common.c
 
-LLVM_C_SOURCES := r600_llvm.c
+LLVM_C_SOURCES = r600_llvm.c

src/mesa/drivers/dri/i915/Makefile.sources

@@ -1,8 +1,8 @@
 # Paths are relative to TOP.
-i915_INCLUDES := \
+i915_INCLUDES = \
 	src/mesa/drivers/dri/intel
 
-i915_C_FILES := \
+i915_C_FILES = \
 	i830_context.c \
 	i830_state.c \
 	i830_texblend.c \

src/mesa/drivers/dri/i965/Makefile.sources

@@ -1,8 +1,8 @@
-i965_INCLUDES := \
+i965_INCLUDES = \
 	$(MESA_TOP)/src \
 	$(MESA_TOP)/src/mesa/drivers/dri/intel
 
-i965_C_FILES := \
+i965_C_FILES = \
 	intel_batchbuffer.c \
 	intel_blit.c \
 	intel_buffer_objects.c \
@@ -111,7 +111,7 @@ i965_C_FILES := \
 	gen7_wm_state.c \
 	gen7_wm_surface_state.c
 
-i965_CXX_FILES := \
+i965_CXX_FILES = \
 	brw_cubemap_normalize.cpp \
 	brw_fs.cpp \
 	brw_fs_cfg.cpp \
@@ -129,4 +129,4 @@ i965_CXX_FILES := \
 	brw_vec4_reg_allocate.cpp \
 	brw_vec4_visitor.cpp
 
-i965_ASM_FILES :=
+i965_ASM_FILES =