loader/libclang: fix CGo-related crash

Sometimes when a GC happens while processing a C fragment with libclang,
a pointer-typed integer with value 0x1 ends up on the Go stack and the
GC will trip over it. This commit changes the offending struct type to
be uintptr_t instead of void*.

See https://go-review.googlesource.com/c/go/+/66332 for a similar
change.

loader/libclang_stubs.c

@@ -0,0 +1,46 @@
+
+// This file implements some small trampoline functions. The signatures
+// are slightly different from the ones defined in libclang.go, but they
+// should be ABI compatible.
+
+#include <clang-c/Index.h> // if this fails, install libclang-8-dev
+
+CXCursor tinygo_clang_getTranslationUnitCursor(CXTranslationUnit tu) {
+	return clang_getTranslationUnitCursor(tu);
+}
+
+unsigned tinygo_clang_visitChildren(CXCursor parent, CXCursorVisitor visitor, CXClientData client_data) {
+	return clang_visitChildren(parent, visitor, client_data);
+}
+
+CXString tinygo_clang_getCursorSpelling(CXCursor c) {
+	return clang_getCursorSpelling(c);
+}
+
+enum CXCursorKind tinygo_clang_getCursorKind(CXCursor c) {
+	return clang_getCursorKind(c);
+}
+
+CXType tinygo_clang_getCursorType(CXCursor c) {
+	return clang_getCursorType(c);
+}
+
+CXCursor tinygo_clang_getTypeDeclaration(CXType t) {
+	return clang_getTypeDeclaration(t);
+}
+
+CXType tinygo_clang_getTypedefDeclUnderlyingType(CXCursor c) {
+	return clang_getTypedefDeclUnderlyingType(c);
+}
+
+CXType tinygo_clang_getCursorResultType(CXCursor c) {
+	return clang_getCursorResultType(c);
+}
+
+int tinygo_clang_Cursor_getNumArguments(CXCursor c) {
+	return clang_Cursor_getNumArguments(c);
+}
+
+CXCursor tinygo_clang_Cursor_getArgument(CXCursor c, unsigned i) {
+	return clang_Cursor_getArgument(c, i);
+}