Merge bitcoin/bitcoin#34589: ci: Temporarily use clang in valgrind tasks

fa70b9ebaa ci: Temporarily use clang in valgrind tasks (MarcoFalke)
faf3ef4ee7 ci: Clarify why valgrind task has gui disabled (MarcoFalke)
fadb77169b test: Scale feature_dbcrash.py timeout with factor (MarcoFalke)

Pull request description:

  valgrind currently does not work on GCC compiled executables, due to an upstream bug. https://bugs.kde.org/show_bug.cgi?id=472329

  So temporarily switch to clang, so that a long term solution can be figured out in the meantime.

ACKs for top commit:
  l0rinc:
    ACK fa70b9ebaa
  fanquake:
    ACK fa70b9ebaa - also checked that it doesn't currently work under aarch64.

Tree-SHA512: 2e7c7a709311efa7bf29c3f9b1db60886b189b2d2bfebb516062163d65f0d7e8de3b6fc21c94cd62f6bd7e786e9c36fba55c4bae956b849851eb8b08e772c03e

test/functional/feature_dbcrash.py

@@ -80,7 +80,7 @@ class ChainstateWriteCrashTest(BitcoinTestFramework):
         after a timeout. Returns the utxo hash of the given node."""
 
         time_start = time.time()
-        while time.time() - time_start < 120:
+        while time.time() - time_start < 120 * self.options.timeout_factor:
             try:
                 # Any of these RPC calls could throw due to node crash
                 self.start_node(node_index)

test/sanitizer_suppressions/valgrind.supp

@@ -12,8 +12,10 @@
 #       --error-limit=no build/bin/test_bitcoin
 #
 # Note that suppressions may depend on OS and/or library versions.
-# Tested on aarch64 and x86_64 with Ubuntu Noble system libs, using clang-16
-# and GCC, without gui.
+# Tested on Debian Trixie system libs,
+# * using clang (only x86_64, see https://bugs.kde.org/show_bug.cgi?id=485276),
+# * and GCC (only -O1, see https://bugs.kde.org/show_bug.cgi?id=472329),
+# without gui (because it only passes with a DEBUG=1 depends build).
 {
    Suppress leaks on shutdown
    Memcheck:Leak