INSTALL.md: add clang for install build dependence

[Bojun-Seo]

clang is not default package of Ubuntu 24.04. So, add clang for install build dependence on INSTALL.md file.

You will get following error during compiling libbpf-tools on Ubuntu 24.04 without this patch.

  MKDIR    .output                                                                          
  BPF      memleak.bpf.o                                                                                                                                                             
/bin/sh: 1: clang: not found
make: *** [Makefile:209: /home/bojun/bcc/libbpf-tools/.output/memleak.bpf.o] Error 127

I guess other Ubuntu versions also need clang for install dependence. But I didn't test it on other versions.

[Bojun-Seo]

I will test this again and change the status to open.

[Bojun-Seo]

I've tested again on freshly installed Ubuntu 24.04 and clang and llvm packages are necessary to build tools in libbpf-tools