[CMake][Fuchsia] Add LLVM_ENABLE_HTTPLIB to Stage 2 build

[aidengrossman]

Summary

This patch sets the LLVM_ENABLE_HTTPLIB flag to ON in the stage 2 build
similar to how many of the other dependency flags are already specified.
This is necessary to configure the stage 2 build by itself, otherwise
the CMake configuration crashes.

This is currently causing the MLGO demo to fail since we're only using
stage 2 to avoid having to build stage 1 to save some compile time.

[phosek]

LGTM

clang/cmake/caches/Fuchsia-stage2.cmake

 # This file sets up a CMakeCache for the second stage of a Fuchsia toolchain build.
 
 option(FUCHSIA_ENABLE_LLDB "Enable LLDB")
 
 set(LLVM_TARGETS_TO_BUILD X86;ARM;AArch64;RISCV CACHE STRING "")
 
 set(PACKAGE_VENDOR Fuchsia CACHE STRING "")
 
 set(_FUCHSIA_ENABLE_PROJECTS "bolt;clang;clang-tools-extra;lld;llvm;polly")
 set(LLVM_ENABLE_RUNTIMES "compiler-rt;libcxx;libcxxabi;libunwind" CACHE STRING "")
 
 set(LLVM_ENABLE_BACKTRACES OFF CACHE BOOL "")
 set(LLVM_ENABLE_DIA_SDK OFF CACHE BOOL "")
+set(LLVM_ENABLE_HTTPLIB ON CACHE BOOL "")
 set(LLVM_ENABLE_LIBCXX ON CACHE BOOL "")
 set(LLVM_ENABLE_LIBEDIT OFF CACHE BOOL "")
 set(LLVM_ENABLE_LLD ON CACHE BOOL "")
 set(LLVM_ENABLE_LTO ON CACHE BOOL "")
 set(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR ON CACHE BOOL "")
 set(LLVM_ENABLE_PLUGINS OFF CACHE BOOL "")
 set(LLVM_ENABLE_TERMINFO OFF CACHE BOOL "")
 set(LLVM_ENABLE_UNWIND_TABLES OFF CACHE BOOL "")