moved clang includes out of /usr/include

sharing a single root leads to an undesirable "clang" completion,
and wasi-sdk keeps the include root separate as well

docker/.clangd

@@ -1,3 +1,3 @@
 Security:
-  AccessibleDirectories: [ "/work/c", "/usr/include" ]
+  AccessibleDirectories: [ "/work/c", "/usr/include", "/usr/lib/clang" ]
 

docker/Dockerfile

@@ -14,7 +14,7 @@ COPY run.sh .
 ADD compile_flags.txt /etc/clangd/compile_flags.txt
 ADD .clang-tidy /work/.clang-tidy
 ADD .clangd /work/.clangd
-RUN cp -alf ./clang/includes /work/c && cp -alf clang/wasi-sdk/share/wasi-sysroot/include /usr && mkdir -p /usr/include/clang/15.0.0 && cp -alf clang/wasi-sdk/lib/clang/15.0.0/include /usr/include/clang/15.0.0
+RUN cp -alf ./clang/includes /work/c && cp -alf clang/wasi-sdk/share/wasi-sysroot/include /usr && mkdir -p /usr/lib/clang/15.0.0 && cp -alf clang/wasi-sdk/lib/clang/15.0.0/include /usr/lib/clang/15.0.0
 RUN addgroup -S appgroup && adduser -S appuser -G appgroup -h /app && chown appuser:appgroup /app
 RUN yarn && yarn build
 EXPOSE $PORT

docker/compile_flags.txt

@@ -1,5 +1,5 @@
 -xc
--isystem/usr/include/clang/15.0.0/include
+-isystem/usr/lib/clang/15.0.0/include
 -Wno-pointer-to-int-cast
 -Wno-int-conversion
 -Werror=implicit-function-declaration