build: check backtrace in libc before searching for execinfo

Use cc.has_function('backtrace', prefix: '#include <execinfo.h>') to check
if backtrace is already available in the default system libraries (such as
glibc on Linux or natively on macOS). If it is available, use a dummy dependency.
Otherwise, fall back to cc.find_library('execinfo', required: false). This prevents
spurious compile or linker failures for unnecessary '-lexecinfo' links on macOS
and other platforms.

Author: fangfufu

meson.build

@@ -42,7 +42,11 @@ fuse_dep = dependency('fuse3')
 uuid_dep = dependency('uuid')
 expat_dep = dependency('expat')
 openssl_dep = dependency('openssl')
-execinfo_dep = cc.find_library('execinfo', required: false)
+if cc.has_function('backtrace', prefix: '#include <execinfo.h>')
+    execinfo_dep = dependency('', required: false)
+else
+    execinfo_dep = cc.find_library('execinfo', required: false)
+endif
 
 httpdirfs_deps = [
     gumbo_dep,