Bugfix: Only use git for build info if the repository is actually the right one

Also adds ability to disable check with BITCOIN_GENBUILD_NO_GIT=1 in the environment

(cherry picked from commit bitcoin/bitcoin@e98e3dde6a)

contrib/gitian-descriptors/gitian-linux.yml

@@ -97,6 +97,7 @@ script: |
   create_per-host_faketime_wrappers "${REFERENCE_DATETIME}"
 
   # Create the release tarball using (arbitrarily) the first host
+  export GIT_DIR="$PWD/.git"
   ./autogen.sh
   CONFIG_SITE=${BASEPREFIX}/`echo "${HOSTS}" | awk '{print $1;}'`/share/config.site ./configure --prefix=/
   make dist

contrib/gitian-descriptors/gitian-osx.yml

@@ -92,6 +92,7 @@ script: |
   create_per-host_faketime_wrappers "${REFERENCE_DATETIME}"
 
   # Create the release tarball using (arbitrarily) the first host
+  export GIT_DIR="$PWD/.git"
   ./autogen.sh
   CONFIG_SITE=${BASEPREFIX}/`echo "${HOSTS}" | awk '{print $1;}'`/share/config.site ./configure --prefix=/
   make dist

contrib/gitian-descriptors/gitian-win.yml

@@ -113,6 +113,7 @@ script: |
   create_per-host_linker_wrapper "${REFERENCE_DATETIME}"
 
   # Create the release tarball using (arbitrarily) the first host
+  export GIT_DIR="$PWD/.git"
   ./autogen.sh
   CONFIG_SITE=${BASEPREFIX}/`echo "${HOSTS}" | awk '{print $1;}'`/share/config.site ./configure --prefix=/
   make dist

share/genbuild.sh

@@ -22,7 +22,7 @@ fi
 
 DESC=""
 SUFFIX=""
-if [ -e "$(which git 2>/dev/null)" -a "$(git rev-parse --is-inside-work-tree 2>/dev/null)" = "true" ]; then
+if [ "${BITCOIN_GENBUILD_NO_GIT}" != "1" -a -e "$(which git 2>/dev/null)" -a "$(git rev-parse --is-inside-work-tree 2>/dev/null)" = "true" -a "$(git status --porcelain -u no --ignored "$0" | cut -b1)" != "?" ]; then
     # clean 'dirty' status of touched files that haven't been modified
     git diff >/dev/null 2>/dev/null