Fix MacOS CI builds (#2354)

- Use container: ubuntu:20.04 instead of container: ubuntu:18.04.
- Add `exp` to `lib_compat.h` to solve the GLIBC 2.29 dependency issue.

Fixes https://github.com/clangd/clangd/issues/2244

.github/workflows/autobuild.yaml

@@ -170,13 +170,13 @@ jobs:
             "-DCMAKE_CXX_COMPILER=clang++"
             "-DLLVM_ENABLE_ZLIB=FORCE_ON"
             "-DCMAKE_OSX_ARCHITECTURES=x86_64;arm64"
-            "-DCMAKE_OSX_DEPLOYMENT_TARGET=10.9"
+            "-DCMAKE_OSX_DEPLOYMENT_TARGET=10.13"
           # BoringSSL doesn't support universal binaries when building with ASM.
           grpc_cmake: >-
             "-DOPENSSL_NO_ASM=ON"
         - name: linux
           os: ubuntu-latest
-          container: ubuntu:18.04
+          container: ubuntu:20.04
           preinstall: >-
             apt-get update &&
             apt-get install -y ninja-build libz-dev libc-ares-dev wget clang-9

.github/workflows/lib_compat.h

@@ -16,5 +16,6 @@ FORCE_SYMBOL_VERSION(expf, GLIBC_2.2.5);
 FORCE_SYMBOL_VERSION(log, GLIBC_2.2.5);
 FORCE_SYMBOL_VERSION(log2, GLIBC_2.2.5);
 FORCE_SYMBOL_VERSION(pow, GLIBC_2.2.5);
+FORCE_SYMBOL_VERSION(exp, GLIBC_2.2.5);
 
 #undef FORCE_SYMBOL_VERSION