Fix wheels' bundled libcurl.so incompatibility with Debian [HACK]

Linux wheels are (currently) built on AlmaLinux, so the libcurl.so
bundled into the wheel follows Alma/Red Hat/Fedora conventions for the
location of its certificate bundle. This fails when the wheel is used on
a Debian/Ubuntu platform with a different convention for this location.
When not overridden by $CURL_CA_BUNDLE, work around this by specifying
the expected Debian bundle location if the Red Hat one isn't present.

Fixes #1257 via a hacky work around.

(Take care to preserve this patch when importing HTSlib in future.)

htslib/hfile_libcurl.c

@@ -34,6 +34,7 @@ DEALINGS IN THE SOFTWARE.  */
 #ifndef _WIN32
 # include <sys/select.h>
 #endif
+#include <sys/stat.h>
 #include <assert.h>
 
 #include "hfile_internal.h"
@@ -1246,6 +1247,19 @@ libcurl_open(const char *url, const char *modes, http_headers *headers)
         if (env_curl_ca_bundle) {
             err |= curl_easy_setopt(fp->easy, CURLOPT_CAINFO, env_curl_ca_bundle);
         }
+#if defined __linux__ && defined BUILDING_WHEEL
+        else {
+            // Linux wheels are (currently) built on AlmaLinux, so the libcurl.so bundled
+            // into the wheel follows Alma/Red Hat/Fedora conventions for the location of
+            // its certificate bundle. This fails when the wheel is used on a Debian/Ubuntu
+            // platform with a different convention for this location. When not overridden
+            // by $CURL_CA_BUNDLE, work around this by specifying the expected Debian bundle
+            // location if the Red Hat one isn't present.
+            struct stat st;
+            if (stat("/etc/pki", &st) < 0 && errno == ENOENT)
+                err |= curl_easy_setopt(fp->easy, CURLOPT_CAINFO, "/etc/ssl/certs/ca-certificates.crt");
+        }
+#endif
     }
     err |= curl_easy_setopt(fp->easy, CURLOPT_USERAGENT, curl.useragent.s);
     if (fp->headers.callback) {

setup.py

@@ -186,6 +186,10 @@ def set_compiler_envvars():
             del os.environ[var]
 
 
+def format_macro_option(name, value):
+    return f"-D{name}={value}" if value is not None else f"-D{name}"
+
+
 def configure_library(library_dir, env_options=None, options=[]):
 
     configure_script = os.path.join(library_dir, "configure")
@@ -532,6 +536,9 @@ def run(self):
 
 define_macros = []
 
+if os.environ.get("CIBUILDWHEEL", "0") == "1":
+    define_macros.append(("BUILDING_WHEEL", None))
+
 suffix = sysconfig.get_config_var('EXT_SUFFIX')
 
 internal_htslib_libraries = [
@@ -567,7 +574,8 @@ def prebuild_libchtslib(ext, force):
             # TODO Eventually by running configure here, we can set these
             # extra flags for configure instead of hacking on ALL_CPPFLAGS.
             args = " ".join(ext.extra_compile_args)
-            run_make(["ALL_CPPFLAGS=-I. " + args + " $(CPPFLAGS)", "lib-static"])
+            defines = " ".join([format_macro_option(*pair) for pair in ext.define_macros])
+            run_make(["ALL_CPPFLAGS=-I. " + args + " " + defines + " $(CPPFLAGS)", "lib-static"])
     else:
         log.warning("skipping 'libhts.a' (already built)")