fix(agc,shader): prime the two host shared mutexes added after 48dcaace7

Commit 48dcaace7 introduced PrimedSharedMutex and converted every host std::shared_mutex that existed at the time, because winpthreads initializes a static rwlock on first use and a concurrent first lock returns EINVAL, which std::shared_mutex ignores (docs/dev/TechnicalDebt.md:10).

Two host mutexes were added afterward and missed the conversion:
- Recompiler.cpp registrationModule() static mutex (added by baf3437465)
- MultisampleTarget.cpp guardedMutex() static mutex (added by d109f3966f)

Apply the same priming. Recompiler.cpp reuses the PrimedSharedMutex already defined in that translation unit; MultisampleTarget.cpp gets the identical local helper to match the existing inline precedent.

Tested: Windows 11 x64, WinLibs GCC 15.2.0 (matches CI). Compiled Recompiler.cpp.obj and all three MultisampleTarget.cpp.obj targets with the project build flags; check_conventions.py passes.

core/libs/prx/libSceAgcDriver/Graphics/src/MultisampleTarget.cpp

@@ -173,8 +173,16 @@ struct GuardedRange {
     std::uint32_t samples;
 };
 
+class PrimedSharedMutex : public std::shared_mutex {
+public:
+    PrimedSharedMutex() {
+        lock();
+        unlock();
+    }
+};
+
 std::shared_mutex& guardedMutex() {
-    static std::shared_mutex mutex;
+    static PrimedSharedMutex mutex;
     return mutex;
 }
 

core/shader/recompiler/Recompiler.cpp

@@ -623,7 +623,7 @@ struct RegistrationModuleEntry {
 std::shared_ptr<const SpecializedModule> registrationModule(std::uint64_t variantId, std::span<const std::uint32_t> moduleKey, const std::function<std::shared_ptr<const SpecializedModule>()>& specialize) {
     std::vector<std::uint64_t> key{variantId};
     key.insert(key.end(), moduleKey.begin(), moduleKey.end());
-    static std::shared_mutex mutex;
+    static PrimedSharedMutex mutex;
     static std::map<std::vector<std::uint64_t>, std::shared_ptr<RegistrationModuleEntry>> modules;
     std::shared_ptr<RegistrationModuleEntry> entry;
     {