ARROW-9789: [C++] Don't install jemalloc in parallel

On ARROW-6437 (apache#7928) we saw occasional "File exists" errors on `jemalloc_ep` on macOS. Googling the error message led back to ARROW-739 (apache#456), which fixed this before by forcing install with `-j1`. ARROW-3492 later made it so jemalloc would build (but not install) in parallel. Then ARROW-3539 (apache#2779) was addressing a problem with that change and, along with fixing the build parallelization issue, unfortunately reverted the original `make -j1 install` fix.

This patch restores the fix from ARROW-739.

Closes apache#7995 from nealrichardson/jemalloc-install

Authored-by: Neal Richardson <neal.p.richardson@gmail.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>

cpp/cmake_modules/ThirdpartyToolchain.cmake

@@ -1454,7 +1454,7 @@ if(ARROW_JEMALLOC)
     BUILD_IN_SOURCE 1
     BUILD_COMMAND ${JEMALLOC_BUILD_COMMAND}
     BUILD_BYPRODUCTS "${JEMALLOC_STATIC_LIB}"
-    INSTALL_COMMAND ${MAKE} install)
+    INSTALL_COMMAND ${MAKE} -j1 install)
 
   # Don't use the include directory directly so that we can point to a path
   # that is unique to our codebase.