Merge pull request #196319 from Homebrew/flang-ci-builds

flang: speed up CI builds

Formula/f/flang.rb

@@ -21,6 +21,7 @@ class Flang < Formula
   end
 
   depends_on "cmake" => :build
+  depends_on "ninja" => :build
   depends_on "llvm"
 
   # Building with GCC fails at linking with an obscure error.
@@ -34,6 +35,7 @@ def install
     llvm = Formula["llvm"]
     # NOTE: Setting `BUILD_SHARED_LIBRARIES=ON` causes the just-built flang to throw ICE.
     args = %W[
+      -G Ninja
       -DCLANG_DIR=#{llvm.opt_lib}/cmake/clang
       -DFLANG_INCLUDE_TESTS=OFF
       -DFLANG_REPOSITORY_STRING=#{tap&.issues_url}
@@ -46,6 +48,8 @@ def install
       -DMLIR_DIR=#{llvm.opt_lib}/cmake/mlir
     ]
     args << "-DFLANG_VENDOR_UTI=sh.brew.flang" if tap&.official?
+    # Linking takes an absurd amount of memory. Try to limit it to no more than 4GB per link job.
+    args << "-DLLVM_RAM_PER_LINK_JOB=#{4 * 1024}" if ENV["HOMEBREW_GITHUB_ACTIONS"].present?
 
     ENV.append_to_cflags "-ffat-lto-objects" if OS.linux? # Unsupported on macOS.
     install_prefix = libexec