clangd: .clangd file that seems to make clangd behave

.clangd

@@ -0,0 +1,18 @@
+CompileFlags:
+  Add:
+    - --target=riscv64-unknown-elf
+    - -mcmodel=medany
+    - -march=rv64gc
+    - -mabi=lp64
+    - -ffreestanding
+    - -fno-common
+    - -nostdlib
+    - -mno-relax
+    - -I.
+    - -Ilib
+    - -fno-stack-protector
+    - -fno-pie
+    - -no-pie
+    - -ggdb
+    - -gdwarf-2
+    - -fno-omit-frame-pointer