Add alias-bootstrap.sh

Contains some useful aliases for Git.

Adds:

- git cmake
- git build
- git crossmake

alias-bootstrap.sh

+#!/usr/bin/env sh
+
+# All these commands can be run from anywhere in the git
+# tree, not just the top level.
+
+# Usage: git cmake
+#
+# Same usage as standard CMake command.
+#
+git config 'alias.cmake' '!cmake'
+
+# Usage: git build <build preset> [options]
+# Usage: git build [options]
+#
+# In the second usage, when no preset is given, the
+# "default" build preset is used.
+#
+# Available options can be found by running:
+#
+#     git cmake --build
+#
+git config 'alias.build' '!p="${1##-*}"; [ "$p" ] && shift; git cmake --build --preset "${p:-default}"'
+
+# Usage: git crossmake
+#
+# Shortcut to i686-w64-mingw32-cmake (CMake cross
+# compiler)
+#
+git config 'alias.crossmake' '!i686-w64-mingw32-cmake'