Fix Abseil CMake package name

It's "absl" not "abseil".

If we use "abseil", -Dabseil_SOURCE=SYSTEM is never succeeded because
abseilConfig.cmake doesn't exist.

This also sets some ABSL_* variables like Velox does in
https://github.com/facebookincubator/velox/blob/main/CMake/resolve_dependency_modules/absl.cmake
.

Author: kou

CMake/abseil.cmake

@@ -0,0 +1,25 @@
+include_guard(GLOBAL)
+
+# TODO: these variables are named VELOX_* because we are piggy-backing on
+# Velox's resolve dependency module for now. We should change and have our own
+# in the future.
+set(VELOX_ABSL_VERSION 20240116.0)
+set(VELOX_ABSL_BUILD_SHA256_CHECKSUM
+    "338420448b140f0dfd1a1ea3c3ce71b3bc172071f24f4d9a57d59b45037da440")
+set(VELOX_ABSL_SOURCE_URL
+    "https://github.com/abseil/abseil-cpp/archive/refs/tags/${VELOX_ABSL_VERSION}.tar.gz"
+)
+
+velox_resolve_dependency_url(ABSL)
+
+message(STATUS "Building Abseil from source")
+
+FetchContent_Declare(
+  absl
+  URL ${VELOX_ABSL_SOURCE_URL}
+  URL_HASH ${VELOX_ABSL_BUILD_SHA256_CHECKSUM})
+
+set(ABSL_BUILD_TESTING OFF)
+set(ABSL_PROPAGATE_CXX_STD ON)
+set(ABSL_ENABLE_INSTALL ON)
+FetchContent_MakeAvailable(absl)

CMake/absl.cmake

@@ -115,8 +115,8 @@ velox_resolve_dependency(Boost 1.77.0 COMPONENTS ${BOOST_INCLUDE_LIBRARIES})
 velox_set_source(folly)
 velox_resolve_dependency(folly)
 
-velox_set_source(abseil)
-velox_resolve_dependency(abseil)
+velox_set_source(absl)
+velox_resolve_dependency(absl)
 
 # Use xxhash and xsimd from Velox for now.
 include_directories(.)