[build] Specify LLVM_MAIN_SRC_DIR when running build-flang.sh

Otherwise Classic Flang's CMakeLists.txt will be unable to find llvm-lit and
cannot generate test-related goals, e.g. `check-all`.

Also fix a typo in build-flang.sh that prevented the option from being passed
to CMake correctly.

.github/workflows/build_flang.yml

@@ -77,7 +77,7 @@ jobs:
       - name: Build and install flang & libpgmath
         run: |
           ${{ env.install_prefix }}/bin/clang --version
-          ./build-flang.sh -t ${{ matrix.target }} -p ${{ env.install_prefix }} -n $(nproc) -c -s -v
+          ./build-flang.sh -t ${{ matrix.target }} -p ${{ env.install_prefix }} -n $(nproc) -c -s -v -l ../../classic-flang-llvm-project/llvm
 
       - name: Copy llvm-lit
         run: |

.github/workflows/build_flang_arm64.yml

@@ -54,7 +54,7 @@ jobs:
       - name: Build and install flang & libpgmath
         run: |
           cd ${{ env.build_path }}/flang
-          ./build-flang.sh -t ${{ matrix.target }} -p ${{ env.install_prefix }} -n `nproc --ignore=1` -v
+          ./build-flang.sh -t ${{ matrix.target }} -p ${{ env.install_prefix }} -n `nproc --ignore=1` -v -l /home/root/classic-flang-llvm-project/llvm
 
       - name: Copy llvm-lit
         run: |

build-flang.sh

@@ -9,7 +9,7 @@ BUILD_TYPE="Release"
 BUILD_PREFIX="./build"
 INSTALL_PREFIX="/usr/local"
 NPROC=1
-USE_LLVM_SRC_ROOT=""
+USE_LLVM_MAIN_SRC_DIR=""
 USE_LLVM_CONFIG=""
 USE_CCACHE="0"
 USE_SUDO="0"
@@ -49,7 +49,7 @@ while getopts "t:d:b:p:n:l:o:csx:v?" opt; do
         b) BUILD_PREFIX=$OPTARG;;
         p) INSTALL_PREFIX=$OPTARG;;
         n) NPROC=$OPTARG;;
-        l) USE_LLVM_SRC_ROOT="-DLLVM_MAIN_SRC_DIR=$OPTARG";;
+        l) USE_LLVM_MAIN_SRC_DIR="-DLLVM_MAIN_SRC_DIR=$OPTARG";;
         o) USE_LLVM_CONFIG="-DLLVM_CONFIG=$OPTARG";;
         c) USE_CCACHE="1";;
         s) USE_SUDO="1";;