feat: allow template specialization

Author: JohelEGP

regression-tests/pure2-template-specialization.cpp2

@@ -0,0 +1,18 @@
+t: @struct <T: type> type = {
+  a: i32 = 1;
+}
+t: @struct <T: type> specialize<T> type requires std::is_void_v<T> = {
+  b: i32 = 2;
+}
+t: @struct specialize<i64> type = {
+  c: i32 = 3;
+}
+v: <T> const i32 = 1;
+v: <> specialize<void> const i32 = 2;
+main: ()   = {
+  [[assert Testing: t<i32>().a == 1]]
+  [[assert Testing: t<void>().b == 2]]
+  [[assert Testing: t<i64>().c == 3]]
+  [[assert Testing: (v<i32>) == 1]]
+  [[assert Testing: (v<void>) == 2]]
+}

regression-tests/test-results/clang-18/clang-version.output

@@ -0,0 +1,4 @@
+clang version 18.0.0 (https://github.com/llvm/llvm-project.git 3723ede3cf5324827f8fbbe7f484c2ee4d7a7204)
+Target: x86_64-pc-linux-gnu
+Thread model: posix
+InstalledDir: /home/johel/root/clang-main/bin

regression-tests/test-results/clang-18/pure2-bugfix-for-non-local-function-expression.cpp.execution

@@ -0,0 +1,3 @@
+sizeof(x) is 25
+(not a name)
+xyz