[PATCH] ci: do not die on deprecated-declarations warning

Like a recent GitHub CI run on linux-musl [1] shows, we seem to be
getting a bunch of errors of the form:

  Error: http.c:1002:9: 'CURLOPT_REDIR_PROTOCOLS' is deprecated:
  since 7.85.0. Use CURLOPT_REDIR_PROTOCOLS_STR
  [-Werror=deprecated-declarations]

For some of them, it may be reasonable to follow the deprecation
notice and update the code, but some symbols like the above is not.

According to the release table [2], 7.85.0 that deprecates
CURLOPT_REDIR_PROTOCOLS was released on 2022-08-31, less than a year
ago, and according to the symbols-in-versions table [3],
CURLOPT_REDIR_PROTOCOLS_STR was introduced in 7.85.0, so it will
make us incompatible with anything older than a year if we rewrote
the call as the message suggests.

Make sure that we won't break the build when -Wdeprecated-declarations
triggers.

[1] https://github.com/git/git/actions/runs/3915509922/jobs/6693756050
[2] https://curl.se/docs/releases.html
[3] https://github.com/curl/curl/blob/master/docs/libcurl/symbols-in-versions

Signed-off-by: Junio C Hamano <redacted>
---
 config.mak.dev | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/config.mak.dev b/config.mak.dev
index 981304727c..afcffa6a04 100644
--- a/config.mak.dev
+++ b/config.mak.dev

@@ -69,6 +69,15 @@ DEVELOPER_CFLAGS += -Wno-missing-braces
 endif
 endif
 
+# Libraries deprecate symbols while retaining them for a long time to
+# keep software working with both older and newer versions of them.
+# Getting warnings does help the developers' awareness, but we cannot
+# afford to update too aggressively.  E.g. CURLOPT_REDIR_PROTOCOLS_STR
+# is only available in 7.85.0 that deprecates CURLOPT_REDIR_PROTOCOLS
+# but we cannot rewrite the uses of the latter with the former until
+# 7.85.0, which was released in August 2022, becomes ubiquitous.
+DEVELOPER_CFLAGS += -Wno-error=deprecated-declarations
+
 # Old versions of clang complain about initializaing a
 # struct-within-a-struct using just "{0}" rather than "{{0}}".  This
 # error is considered a false-positive and not worth fixing, because

-- 
2.39.0-198-ga38d39a4c5