Various dlopen/linking cleanups from #42100 (#42166)

- **bpf-util: rename from bpf-dlopen, unify version-specific symbol
handling**
- **cryptsetup: dlopen libcryptsetup in tokens**
- **tree-wide: dlopen libpam in pam plugins**
- **test-bus-marshal: dlopen() glib and libdbus instead of linking
directly**
- **lock-util: Simplify timeout for lock_generic_with_timeout()**
- **color-util: simplify hsv_to_rgb, fix rgb_to_hsv negative-hue wrap**
- **tree-wide: Use our own macros instead of fabs()/fmax()/fmin()**
- **locale-util: dlopen() libintl instead of linking against it**
- **home: Use log2u64() over log2()**
- **meson: drop libdl, threads, and librt dependencies**
- **libc: Use dlsym() from a constructor instead of weak symbols**
- **libc: Make sure C23 versions of strtol(), sscanf() are not used**

src/include/glibc/stdio.h

@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+/* Force glibc's stdio.h to route sscanf/fscanf to the old __isoc99_* siblings (GLIBC_2.7) rather
+ * than the newer __isoc23_* ones (GLIBC_2.38). The only behavioural difference is "0b" prefix
+ * support in %i conversions, which we don't use. We include features.h first so the macro is set
+ * to its normal value, then override it before stdio.h's body evaluates __GLIBC_USE(C23_STRTOL).
+ *
+ * The macro was named __GLIBC_USE_C2X_STRTOL on glibc 2.38–2.39 and renamed to the C23 spelling
+ * in glibc 2.40; clear both so this override works across that range. */
+
+#include <features.h>
+#undef __GLIBC_USE_C2X_STRTOL
+#define __GLIBC_USE_C2X_STRTOL 0
+#undef __GLIBC_USE_C23_STRTOL
+#define __GLIBC_USE_C23_STRTOL 0
+
+#include_next <stdio.h>      /* IWYU pragma: export */

src/include/glibc/stdlib.h

@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+/* Force glibc's stdlib.h to leave strtol/strtoul/strtoll/strtoull as their original GLIBC_2.2.5
+ * symbols rather than redirect to __isoc23_* (GLIBC_2.38). The only behavioural difference is
+ * "0b" prefix support in base 0/2 parsing, which we don't use.
+ *
+ * The macro was named __GLIBC_USE_C2X_STRTOL on glibc 2.38–2.39 and renamed to the C23 spelling
+ * in glibc 2.40; clear both so this override works across that range. */
+
+#include <features.h>
+#undef __GLIBC_USE_C2X_STRTOL
+#define __GLIBC_USE_C2X_STRTOL 0
+#undef __GLIBC_USE_C23_STRTOL
+#define __GLIBC_USE_C23_STRTOL 0
+
+#include_next <stdlib.h>     /* IWYU pragma: export */