Evas GL common: Skip shaders generation if there is no change

Based on a quick git diff we check that the glsl code has not changed.
This should fix out-of-tree builds and avoid all source modification
unless required.

When compiling from a tarball there should be no git tree (err 129),
or if there's one the files should not be checked in (ie. no diff).
If you changed the glsl files in a tarball... too bad for you.

If this is still not enough to fix the build, then go ahead and disable
the script from Makefile_Evas.am

I would like to note that the auto-generation during make is extremely
useful when working on the shaders, which is why I'd rather keep it enabled.

@fix

src/modules/evas/engines/gl_common/shader/evas_gl_enum.x

@@ -1,5 +1,4 @@
-/* DO NOT MODIFY THIS FILE AS IT IS AUTO-GENERATED
- * See: ./modules/evas/engines/gl_common/shader/gen_shaders.sh */
+/* DO NOT MODIFY THIS FILE AS IT IS AUTO-GENERATED */
 
 typedef enum {
    SHADER_RECT,

src/modules/evas/engines/gl_common/shader/evas_gl_shaders.x

@@ -1,5 +1,4 @@
-/* DO NOT MODIFY THIS FILE AS IT IS AUTO-GENERATED
- * See: ./modules/evas/engines/gl_common/shader/gen_shaders.sh */
+/* DO NOT MODIFY THIS FILE AS IT IS AUTO-GENERATED */
 
 #include "../evas_gl_private.h"
 

src/modules/evas/engines/gl_common/shader/gen_shaders.sh

@@ -35,6 +35,14 @@ precision mediump float;
 #endif
 "
 
+# Skip generation if there is no diff (or no git)
+if ! git rev-parse 2>> /dev/null >> /dev/null ; then exit 0 ; fi
+if git diff --quiet --exit-code -- "$DIR"
+then
+  touch "${OUTPUT}" "${OUTPUT_ENUM}"
+  exit 0
+fi
+
 function upper() {
   echo $@ |tr '[:lower:]' '[:upper:]'
 }
@@ -50,7 +58,7 @@ IFS=$'\n' SHADERS=(`cat ${DIR}/shaders.txt`)
 IFS=$OIFS
 
 # Write header
-printf "/* DO NOT MODIFY THIS FILE AS IT IS AUTO-GENERATED\n * See: $0 */\n\n" > ${OUTPUT}
+printf "/* DO NOT MODIFY THIS FILE AS IT IS AUTO-GENERATED */\n\n" > ${OUTPUT}
 
 # Including private for hilights and stuff :)
 printf "#include \"../evas_gl_private.h\"\n\n" >> ${OUTPUT}
@@ -164,7 +172,7 @@ static const struct {
 
 printf "${shaders_source}};\n\n" >> ${OUTPUT}
 
-printf "/* DO NOT MODIFY THIS FILE AS IT IS AUTO-GENERATED\n * See: $0 */
+printf "/* DO NOT MODIFY THIS FILE AS IT IS AUTO-GENERATED */
 
 typedef enum {
 ${shaders_enum}   SHADER_LAST

src/modules/evas/engines/gl_common/shader_3d/evas_gl_3d_shaders.x

@@ -1,5 +1,4 @@
-/* DO NOT MODIFY THIS FILE AS IT IS AUTO-GENERATED
- * See: modules/evas/engines/gl_common/shader_3d/gen_shaders_3d.sh */
+/* DO NOT MODIFY THIS FILE AS IT IS AUTO-GENERATED */
 
 static const char vertex_color_vert_glsl[] =
    "#ifdef GL_ES\n"

src/modules/evas/engines/gl_common/shader_3d/gen_shaders_3d.sh

@@ -6,6 +6,14 @@ DIR=`dirname $0`
 
 OUTPUT=${DIR}/evas_gl_3d_shaders.x
 
+# Skip generation if there is no diff (or no git)
+if ! git rev-parse 2>> /dev/null >> /dev/null ; then exit 0 ; fi
+if git diff --quiet --exit-code -- "$DIR"
+then
+  touch "${OUTPUT}"
+  exit 0
+fi
+
 exec 1<&-
 exec 1>${OUTPUT}
 
@@ -14,7 +22,7 @@ vert_shaders_source=""
 frag_shaders_source=""
 
 # Write header
-printf "/* DO NOT MODIFY THIS FILE AS IT IS AUTO-GENERATED\n * See: $0 */\n\n"
+printf "/* DO NOT MODIFY THIS FILE AS IT IS AUTO-GENERATED */\n\n"
 for shd in ${SHADERS} ; do
   lname=`basename ${shd} .shd`