CMakeLists.txt fix spacing
Fix cmakelint issues "./src/CMakeLists.txt:136: Weird indentation; use 2 spaces [whitespace/indent]
./src/CMakeLists.txt:137: Weird indentation; use 2 spaces [whitespace/indent]
./src/CMakeLists.txt:172: Extra spaces between 'if' and its () [whitespace/extra]
./CMakeLists.txt:61: Extra spaces between 'if' and its () [whitespace/extra]".