clang-16 is useless and break the sparse build

[avolkov-1221]

Hello,

The latest Docker images were switched to clang-16 installation, however this clang is not used by the system as Ubuntu's clang-15 is installed by default by mono dependencies, so clang-16 is probably nothing but a waste of space.

Also, if the default clang-15 is replaced to clang-16 by the update-alternative script, then the sparse-llvm build will be broken as no one has updated it for years. Part of sparse-llvm broken build log is below.

So I suggest to switch back to Ubuntu's clang-15 usage, of fix sparse-llvm and forcing clang-16 as as the only clang of the system.

Broken sparse-llvm:

......
  CC      version.o
sparse-llvm.c: In function ‘get_sym_value’:
sparse-llvm.c:305:34: warning: implicit declaration of function ‘LLVMConstGEP’; did you mean ‘LLVMConstGEP2’? [-Wimplicit-function-declaration]
  305 |                         result = LLVMConstGEP(data, indices, ARRAY_SIZE(indices));
      |                                  ^~~~~~~~~~~~
      |                                  LLVMConstGEP2
sparse-llvm.c:305:32: warning: assignment to ‘LLVMValueRef’ {aka ‘struct LLVMOpaqueValue *’} from ‘int’ makes pointer from integer without a cast [-Wint-conversion]
  305 |                         result = LLVMConstGEP(data, indices, ARRAY_SIZE(indices));
      |                                ^
sparse-llvm.c: In function ‘calc_gep’:
sparse-llvm.c:488:16: warning: implicit declaration of function ‘LLVMBuildInBoundsGEP’; did you mean ‘LLVMBuildInBoundsGEP2’? [-Wimplicit-function-declaration]
  488 |         addr = LLVMBuildInBoundsGEP(builder, base, &off, 1, name);
      |                ^~~~~~~~~~~~~~~~~~~~
      |                LLVMBuildInBoundsGEP2
sparse-llvm.c:488:14: warning: assignment to ‘LLVMValueRef’ {aka ‘struct LLVMOpaqueValue *’} from ‘int’ makes pointer from integer without a cast [-Wint-conversion]
  488 |         addr = LLVMBuildInBoundsGEP(builder, base, &off, 1, name);
      |              ^
sparse-llvm.c: In function ‘output_op_load’:
sparse-llvm.c:714:18: warning: implicit declaration of function ‘LLVMBuildLoad’; did you mean ‘LLVMBuildLoad2’? [-Wimplicit-function-declaration]
  714 |         target = LLVMBuildLoad(fn->builder, addr, name);
      |                  ^~~~~~~~~~~~~
      |                  LLVMBuildLoad2
sparse-llvm.c:714:16: warning: assignment to ‘LLVMValueRef’ {aka ‘struct LLVMOpaqueValue *’} from ‘int’ makes pointer from integer without a cast [-Wint-conversion]
  714 |         target = LLVMBuildLoad(fn->builder, addr, name);
      |                ^
sparse-llvm.c: In function ‘output_op_call’:
sparse-llvm.c:822:18: warning: implicit declaration of function ‘LLVMBuildCall’; did you mean ‘LLVMBuildCall2’? [-Wimplicit-function-declaration]
  822 |         target = LLVMBuildCall(fn->builder, func, args, n_arg, name);
      |                  ^~~~~~~~~~~~~
      |                  LLVMBuildCall2
sparse-llvm.c:822:16: warning: assignment to ‘LLVMValueRef’ {aka ‘struct LLVMOpaqueValue *’} from ‘int’ makes pointer from integer without a cast [-Wint-conversion]
  822 |         target = LLVMBuildCall(fn->builder, func, args, n_arg, name);
      |                ^
  AR      libsparse.a
  LD      compile
  LD      ctags
  LD      example
  LD      graph
  LD      obfuscate
  LD      sparse
  LD      test-dissect
  LD      test-lexing
  LD      test-linearize
  LD      test-parsing
  LD      test-show-type
  LD      test-unssa
  LD      c2xml
  LD      sparse-llvm
/usr/bin/ld: sparse-llvm.o: in function `get_sym_value':
.../sparse/sparse/sparse-llvm.c:305: undefined reference to `LLVMConstGEP'
/usr/bin/ld: sparse-llvm.o: in function `calc_gep':
.../sparse/sparse/sparse-llvm.c:488: undefined reference to `LLVMBuildInBoundsGEP'
/usr/bin/ld: sparse-llvm.o: in function `output_op_load':
.../sparse/sparse/sparse-llvm.c:714: undefined reference to `LLVMBuildLoad'
/usr/bin/ld: sparse-llvm.o: in function `output_op_call':
.../sparse/sparse/sparse-llvm.c:822: undefined reference to `LLVMBuildCall'
collect2: error: ld returned 1 exit status
make: *** [Makefile:250: sparse-llvm] Error 1