[flang] Fix DYLIB builds

https://reviews.llvm.org/D120568 broke builds that set
both `LLVM_BUILD_LLVM_DYLIB` and `LLVM_LINK_LLVM_DYLIB`. This patch
fixes that.

The build failure was caused by the fact that some LLVM libraries (which
are also LLVM components) were listed directly as link-time dependencies
instead of using `LINK_COMPONENTS` in CMake files. This lead to a linker
invocation like this (simplified version to demonstrate the problem):
```
ld lib/libLLVM.so lib/libLLVMAnalysis.a lib/libLLVMTarget.a
```
That's problematic and unnecessary because `libLLVM.so` incorporates
`libLLVMAnalysis` and `libLLVMTarget`. A correct invocation would look
like this (`LLVM_LINK_LLVM_DYLIB` _is not_ set):
```
ld  lib/libLLVMAnalysis.a lib/libLLVMTarget.a
```
or this (`LLVM_LINK_LLVM_DYLIB` _is_ set):
```
ld lib/libLLVM.so
```

Differential Revision: https://reviews.llvm.org/D121461