[Fuchsia] Do not enable the Z3 solver for a fuchsia toolchain

[leonardchan]

Summary

Some workstations may not be using a compatible version of Z3, leading to:

[118/3622] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/Z3Solver.cpp.o
FAILED: lib/Support/CMakeFiles/LLVMSupport.dir/Z3Solver.cpp.o 
/usr/local/google/home/leonardchan/goma/gomacc /usr/local/google/home/leonardchan/llvm-monorepo/llvm-build-3-two-stage-fuchsia-toolchain/./bin/clang++ --sysroot=/usr/local/google/home/leonardchan/sysroot/linux-amd64  -DGTEST_HAS_RTTI=0 -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -Ilib/Support -I/usr/local/google/home/leonardchan/llvm-monorepo/llvm-project-3/llvm/lib/Support -I/usr/local/google/home/leonardchan/misc/libxml2-install/include/libxml2 -Iinclude -I/usr/local/google/home/leonardchan/llvm-monorepo/llvm-project-3/llvm/include -I/usr/local/google/home/leonardchan/misc/zlib-install/include -fPIC -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wno-comment -Wstring-conversion -fdiagnostics-color -ffunction-sections -fdata-sections -flto -ffile-prefix-map=/usr/local/google/home/leonardchan/llvm-monorepo/llvm-build-3-two-stage-fuchsia-toolchain/tools/clang/stage2-bins=../llvm-build-3-two-stage-fuchsia-toolchain/tools/clang/stage2-bins -ffile-prefix-map=/usr/local/google/home/leonardchan/llvm-monorepo/llvm-project-3/= -no-canonical-prefixes -O3 -DNDEBUG   -std=c++14  -fno-exceptions -fno-unwind-tables -fno-asynchronous-unwind-tables -fno-rtti -MD -MT lib/Support/CMakeFiles/LLVMSupport.dir/Z3Solver.cpp.o -MF lib/Support/CMakeFiles/LLVMSupport.dir/Z3Solver.cpp.o.d -o lib/Support/CMakeFiles/LLVMSupport.dir/Z3Solver.cpp.o -c /usr/local/google/home/leonardchan/llvm-monorepo/llvm-project-3/llvm/lib/Support/Z3Solver.cpp
/usr/local/google/home/leonardchan/llvm-monorepo/llvm-project-3/llvm/lib/Support/Z3Solver.cpp:18:10: fatal error: 'z3.h' file not found
#include <z3.h>
         ^~~~~~
1 error generated.

when building locally. Our prod clang builders don't seem to be using this, so we don't need this locally either.

[phosek]

LGTM, don't forget to include full context with your patches.

clang/cmake/caches/Fuchsia-stage2.cmake

 set(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR ON CACHE BOOL "")
 set(LLVM_ENABLE_TERMINFO OFF CACHE BOOL "")
 set(LLVM_ENABLE_UNWIND_TABLES OFF CACHE BOOL "")
 set(LLVM_ENABLE_ZLIB ON CACHE BOOL "")
 set(LLVM_INCLUDE_DOCS OFF CACHE BOOL "")
 set(LLVM_INCLUDE_EXAMPLES OFF CACHE BOOL "")
 set(LLVM_INCLUDE_GO_TESTS OFF CACHE BOOL "")
 set(LLVM_USE_RELATIVE_PATHS_IN_FILES ON CACHE BOOL "")
+set(LLVM_ENABLE_Z3_SOLVER OFF CACHE BOOL "")
 
 set(CLANG_DEFAULT_CXX_STDLIB libc++ CACHE STRING "")
 if(NOT APPLE)
   set(CLANG_DEFAULT_LINKER lld CACHE STRING "")
   set(CLANG_DEFAULT_OBJCOPY llvm-objcopy CACHE STRING "")
 endif()
 set(CLANG_DEFAULT_RTLIB compiler-rt CACHE STRING "")
 set(CLANG_ENABLE_ARCMT OFF CACHE BOOL "")