Allow git repo as argument to build script

This will help build server perform builds with copy of repo in a folder
outside the original git repo folder. Also testing signed commits on
GitHub.

build.bash

@@ -4,16 +4,20 @@
 #
 # Usage:
 #
-#     $ ./build.bash [output_filename]
+#     $ ./build.bash [output_filename] [git_repo]
 #
 # Outputs compiled program in current directory.
 # Default file name is 'ecaddy'.
+# Default git repo is current directory.
+# Builds always take place from current directory.
 
 set -euo pipefail
 
 : ${output_filename:="${1:-}"}
 : ${output_filename:="ecaddy"}
 
+: ${git_repo:="${2:-}"}
+
 pkg=main
 ldflags=()
 
@@ -25,28 +29,28 @@ ldflags+=("-X" "\"${name}=${value}\"")
 # Current tag, if HEAD is on a tag
 name="${pkg}.gitTag"
 set +e
-value="$(git describe --exact-match HEAD 2>/dev/null)"
+value="$(git -C "${git_repo}" describe --exact-match HEAD 2>/dev/null)"
 set -e
 ldflags+=("-X" "\"${name}=${value}\"")
 
 # Nearest tag on branch
 name="${pkg}.gitNearestTag"
-value="$(git describe --abbrev=0 --tags HEAD)"
+value="$(git -C "${git_repo}" describe --abbrev=0 --tags HEAD)"
 ldflags+=("-X" "\"${name}=${value}\"")
 
 # Commit SHA
 name="${pkg}.gitCommit"
-value="$(git rev-parse --short HEAD)"
+value="$(git -C "${git_repo}" rev-parse --short HEAD)"
 ldflags+=("-X" "\"${name}=${value}\"")
 
 # Summary of uncommitted changes
 name="${pkg}.gitShortStat"
-value="$(git diff-index --shortstat HEAD)"
+value="$(git -C "${git_repo}" diff-index --shortstat HEAD)"
 ldflags+=("-X" "\"${name}=${value}\"")
 
 # List of modified files
 name="${pkg}.gitFilesModified"
-value="$(git diff-index --name-only HEAD)"
+value="$(git -C "${git_repo}" diff-index --name-only HEAD)"
 ldflags+=("-X" "\"${name}=${value}\"")
 
 go build -ldflags "${ldflags[*]}" -o "${output_filename}"