[Bug]: Curl/URL module does not work with LLVM backend

[jabraham17]

The following code fails to compile with the LLVM backend.

import URL;
var r = URL.openUrlReader("http://www.example.com");

$CHPL_HOME/modules/packages/Curl.chpl:159: In module 'Curl':
$CHPL_HOME/modules/packages/Curl.chpl:399: error: Could not find C variable CURLPAUSE_CONT - perhaps it is a complex macro?

However, when using the C backend this compiles and works properly. The root cause of this is that the LLVM backend can't have extern variables to macros (as the error message suggests), and so a fix for this issue would be to just have that support. However, I could not find a relevant existing issue for that feature request, and so instead am treating this as a bug with URL/Curl.

Chplenv

CHPL_TARGET_PLATFORM: darwin
CHPL_TARGET_COMPILER: llvm
CHPL_TARGET_ARCH: arm64
CHPL_TARGET_CPU: native *
CHPL_LOCALE_MODEL: flat
CHPL_COMM: none
CHPL_TASKS: qthreads
CHPL_LAUNCHER: none
CHPL_TIMERS: generic
CHPL_UNWIND: none
CHPL_MEM: jemalloc
CHPL_ATOMICS: cstdlib
CHPL_GMP: system *
CHPL_HWLOC: bundled *
CHPL_RE2: bundled *
CHPL_LLVM: system
CHPL_AUX_FILESYS: none

Chplenv with C backend

CHPL_TARGET_PLATFORM: darwin
CHPL_TARGET_COMPILER: clang *
CHPL_TARGET_ARCH: arm64
CHPL_TARGET_CPU: native *
CHPL_LOCALE_MODEL: flat
CHPL_COMM: none
CHPL_TASKS: qthreads
CHPL_LAUNCHER: none
CHPL_TIMERS: generic
CHPL_UNWIND: none
CHPL_MEM: jemalloc
CHPL_ATOMICS: cstdlib
CHPL_GMP: system *
CHPL_HWLOC: bundled *
CHPL_RE2: bundled *
CHPL_LLVM: system
CHPL_AUX_FILESYS: none

[mppf]

The root cause of this is that the LLVM backend can't have extern variables to macros (as the error message suggests)

Actually it can if they are simple enough. Either way, the issue is the same here.