editorconfig: add indentation rules

Commands used to list the file extensions used in the project:

    $ git ls-files | sed -En 's/.*(\.[^.]+)$/\1/p' |
      LC_ALL=C sort | uniq -c

For rules that are more specific to a given directory, put a dedicated
.editorconfig file in it.

1 files changed, 27 insertions, 0 deletions

diff --git a/.editorconfig b/.editorconfig
index f999431de..7d98c1b14 100644
--- a/.editorconfig
+++ b/.editorconfig
@@ -5,3 +5,30 @@ charset = utf-8
 end_of_line = lf
 insert_final_newline = true
 trim_trailing_whitespace = true
+
+# Build
+[configure.ac]
+indent_size = 8
+indent_style = tab
+
+[*{.mk,Makefile}{,.in}]
+indent_size = 8
+indent_style = tab
+
+# Source code and scripts
+[*.{c,h}{,.in}]
+indent_size = 8
+indent_style = tab
+
+[*.{awk,exp,sh}{,.in}]
+indent_size = 8
+indent_style = tab
+
+[*.py{,.in}]
+indent_size = 4
+indent_style = space
+
+# Misc
+[.gitlab-ci.yml]
+indent_size = 4
+indent_style = space