[tools][remarks-shlib] Don't build libRemarks.so without PIC

A build on `sparcv9-sun-solaris2.11` with `-DLLVM_ENABLE_PIC=Off` failed
linking `libRemarks.so`:

  [27/2297] Linking CXX shared library lib/libRemarks.so.12git
  FAILED: lib/libRemarks.so.12git
  [...]
  ld: fatal: relocation error: R_SPARC_H44: file lib/libLLVMRemarks.a(Remark.cpp.o): symbol _ZTVN4llvm18raw_string_ostreamE: invalid shared object relocation type: ABS44 code model unsupported
  [...]

On Solaris/sparcv9 as on many other targets you cannot link non-PIC objects
into a shared object.

The following patch avoids this by not building the library with PIC.  It
allowed the build to complete and `ninja check-all` showed no errors.

Differential Revision: https://reviews.llvm.org/D85626