Fix: gcc-armhf not reproducible (#64) (#333)

libstdc++.a from gcc-armhf was not reproducible on Travis (it was, when built locally!). These .a files are just archives of object files .o, and in this case it was caused by a random order of the .o files in the archive.

This PR patches the package() function of the APKBUILD when running pmbootstrap aportgen gcc-armhf (same for aarch64 of course), to extract all .a files, and repack them to be reproducible (by sorting the files before packing them).

As usually, we can still inherit everything from the upstream gcc aport from Alpine, and apply our changes on top of that.

Travis without the patch:
https://api.travis-ci.org/jobs/260402679/log.txt?deansi=true

> CHALLENGE FAILED for usr/armv6-alpine-linux-muslgnueabihf/lib/libstdc++.a:File 'usr/armv6-alpine-linux-muslgnueabihf/lib/libstdc++.a' is different!

Travis with the patch (I've instructed Travis to run off this branch to test it):
https://api.travis-ci.org/jobs/260806203/log.txt?deansi=true

> Done. Your build exited with 0.

cross/gcc-aarch64/APKBUILD

@@ -321,6 +321,26 @@ build() {
 }
 
 package() {
+            # Repack the *.a files to be reproducible (see #64)
+            _temp="$_builddir"/_reproducible-patch
+            cd "$_builddir"
+            for f in $(find -name '*.a'); do
+                # Copy to a temporary folder
+                echo "Repack $f to be reproducible"
+                mkdir -p "$_temp"
+                cd "$_temp"
+                cp "$_builddir"/"$f" .
+
+                # Repack with a sorted file order
+                ar x *.a
+                rm *.a
+                ar r sorted.a $(find -name '*.o' | sort)
+
+                # Copy back and clean up
+                cp -v sorted.a "$_builddir"/"$f"
+                cd ..
+                rm -r "$_temp"
+            done
 	cd "$_builddir"
 	make -j1 DESTDIR="${pkgdir}" install
 

cross/gcc-armhf/APKBUILD

@@ -321,6 +321,26 @@ build() {
 }
 
 package() {
+            # Repack the *.a files to be reproducible (see #64)
+            _temp="$_builddir"/_reproducible-patch
+            cd "$_builddir"
+            for f in $(find -name '*.a'); do
+                # Copy to a temporary folder
+                echo "Repack $f to be reproducible"
+                mkdir -p "$_temp"
+                cd "$_temp"
+                cp "$_builddir"/"$f" .
+
+                # Repack with a sorted file order
+                ar x *.a
+                rm *.a
+                ar r sorted.a $(find -name '*.o' | sort)
+
+                # Copy back and clean up
+                cp -v sorted.a "$_builddir"/"$f"
+                cd ..
+                rm -r "$_temp"
+            done
 	cd "$_builddir"
 	make -j1 DESTDIR="${pkgdir}" install