[android] Put in fixes for librt and armv7-a

Android doesn't have a separate librt, it's just part of libc. Also, the static
build wasn't working for armv7-a, because the test executables wouldn't link
with the multiple definition errors listed in android/ndk#176, so use the
workaround given there.

Author: finagolfin

CMakeLists.txt

@@ -113,7 +113,9 @@ if(__BUILTIN_TRAP)
   set(HAVE_NORETURN_BUILTIN_TRAP 1)
 endif()
 
-find_package(LibRT)
+if(NOT CMAKE_SYSTEM_NAME STREQUAL Android)
+  find_package(LibRT)
+endif()
 
 check_function_exists(_pthread_workqueue_init HAVE__PTHREAD_WORKQUEUE_INIT)
 check_function_exists(getprogname HAVE_GETPROGNAME)

tests/CMakeLists.txt

@@ -88,6 +88,14 @@ function(add_unit_test name)
     target_compile_options(${name} PRIVATE -fblocks)
     target_compile_options(${name} PRIVATE -Wall -Wno-deprecated-declarations)
   endif()
+  # Without this flag, cross-compiling static test executables for Android armv7
+  # fails with the multiple definition errors seen in android/ndk#176, so I
+  # pulled in this workaround noted there. The tests build and run with this
+  # flag applied.
+  if(NOT BUILD_SHARED_LIBS AND CMAKE_SYSTEM_NAME STREQUAL Android AND
+     CMAKE_SYSTEM_PROCESSOR STREQUAL armv7-a)
+    target_link_options(${name} PRIVATE "LINKER:--allow-multiple-definition")
+  endif()
   target_link_libraries(${name}
                         PRIVATE
                           dispatch