[CMake] Disable exceptions in cpp-httplib

[aidengrossman]

Summary

This patch disables exceptions in cpp-httplib which are turned on by
default and only disabled through the use of a preprocessor macro.

[aidengrossman]

I'm not totally sure why this is popping up on my system and doesn't appear at all in the Fuchsia builds, because exceptions have been in cpp-httplib for a while and since it is a header only (at least in the default configuration) and needs this flag defined to disable features. I don't think it's being built as a shared library with exceptions turned off at that stage?

[phosek]

Thanks for catching this, I'm also not sure why this doesn't come up in our build. I think it'd be cleaner to provide a CMake option to disable exceptions in the generated CMake package, I created https://github.com/yhirose/cpp-httplib/pull/1580 that implements that.

[aidengrossman]

Thanks for looking into this! Disabling it in the generated CMake package definitely does seem like the cleaner option.

llvm/lib/Debuginfod/CMakeLists.txt

 # Link LibCURL if the user wants it
 if (LLVM_ENABLE_CURL)
   set(imported_libs CURL::libcurl)
 endif()
 
 # Link cpp-httplib if the user wants it
 if (LLVM_ENABLE_HTTPLIB)
   set(imported_libs ${imported_libs} httplib::httplib)
 endif()
 
 # Make sure pthread is linked if this is a unix host
 if (CMAKE_HOST_UNIX)
   set(imported_libs ${imported_libs} ${LLVM_PTHREAD_LIB})
 endif()
 
+# cpp-httplib by default builds with exceptions unless they are disabled using
+# a preprocessor macro.
+if (LLVM_ENABLE_HTTPLIB)
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -DCPPHTTPLIB_NO_EXCEPTIONS")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DCPPHTTPLIB_NO_EXCEPTIONS")
+endif()
+
 # Note: This isn't a component, since that could potentially add a libcurl
 # dependency to libLLVM.
 add_llvm_library(LLVMDebuginfod
   BuildIDFetcher.cpp
   Debuginfod.cpp
   HTTPClient.cpp
   HTTPServer.cpp