Merge bitcoin/bitcoin#27301: depends: make fontconfig build under clang-16

9cbc1c2 depends: make fontconfig build under clang-16 (fanquake)

Pull request description:

  Use the same workaround we've applied to qrencode, and other packages. Fontconfig not building is currently a blocker for fuzz/sanitizer infra upgrades (#27298).

  For now, this is also more straightforward than bumping the package, which introduces more complexity/usage of gperf.

  Closes: #27299.

ACKs for top commit:
  hebasto:
    ACK 9cbc1c2

Tree-SHA512: 387ea1a73e3429f166ef5278305a56cb3c69b6e3fc8a21a66521738e313e3fe783f042759b396cd88e28c10918a4427fb836a8dfecc5a846723b6f6c6a7ade51

Author: fanquake

depends/packages/fontconfig.mk

@@ -9,6 +9,7 @@ $(package)_patches=gperf_header_regen.patch
 define $(package)_set_vars
   $(package)_config_opts=--disable-docs --disable-static --disable-libxml2 --disable-iconv
   $(package)_config_opts += --disable-dependency-tracking --enable-option-checking
+  $(package)_cflags += -Wno-implicit-function-declaration
 endef
 
 define $(package)_preprocess_cmds