build: disable most built-in implicit make rules

Clear `.SUFFIXES:` to reduce unnecessary filesystem lookups.

Overall, this appears to reduce the amount of implicit rule searches by
~62% for the default build and by ~96% for the "man" target (as an
example):

    $ git checkout master >/dev/null 2>&1
    $ git show --pretty='%h %ai %s' -s
    a8f01a383 2023-06-20 05:26:23 +0000 Merge pull request #5859 from kmk3/build-remove-retpoline
    $ ./configure >/dev/null
    $ make clean >/dev/null && make --debug=i -j 4     | grep -F 'Trying implicit' | wc -l
    6798
    $ make clean >/dev/null && make --debug=i -j 4 man | grep -F 'Trying implicit' | wc -l
    1085
    # (with this commit applied)
    $ make clean >/dev/null && make --debug=i -j 4     | grep -F 'Trying implicit' | wc -l
    2535
    $ make clean >/dev/null && make --debug=i -j 4 man | grep -F 'Trying implicit' | wc -l
    42

Environment: GNU make 4.4.1-2 on Artix Linux.

Commands used to search and replace:

    $ git ls-files -z -- '*Makefile*' | xargs -0 -I '{}' sh -c \
      "printf '%s\n' \"\$(sed '1s/^/.SUFFIXES:\n/' '{}')\" >'{}'"

See also commit f48886f25 ("build: mark most phony targets as such",
2023-02-01) / PR #5637.

1 files changed, 1 insertions, 0 deletions

diff --git a/test/Makefile b/test/Makefile
index 2f023b8b1..08462c09b 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -1,3 +1,4 @@
+.SUFFIXES:
 ROOT = ..
 -include $(ROOT)/config.mk