Remove parallel stl sort and revert to std++11

CMakeLists.txt

@@ -163,10 +163,10 @@ if (PPC64 OR SPARC OR ZARCH)
 endif ()
 
 set(MMSEQS_C_FLAGS "${MMSEQS_CXX_FLAGS}")
-set(MMSEQS_CXX_FLAGS "${MMSEQS_CXX_FLAGS} -std=c++17")
+set(MMSEQS_CXX_FLAGS "${MMSEQS_CXX_FLAGS} -std=c++1y")
 # Compiler-specific features
 if (CMAKE_COMPILER_IS_CLANG AND (NOT EMSCRIPTEN))
-    set(CMAKE_XCODE_ATTRIBUTE_CLANG_CXX_LANGUAGE_STANDARD "c++17")
+    set(CMAKE_XCODE_ATTRIBUTE_CLANG_CXX_LANGUAGE_STANDARD "c++11")
     set(CMAKE_XCODE_ATTRIBUTE_CLANG_CXX_LIBRARY "libc++")
     set(MMSEQS_CXX_FLAGS "${MMSEQS_CXX_FLAGS} -stdlib=libc++")
 endif ()

src/commons/FastSort.h

@@ -1,7 +1,4 @@
 #include <algorithm>
-#if __has_include(<execution>) //checking to see if the <execution> header is there
-#include <execution>
-#endif
 
 #ifdef ENABLE_IPS4O
 # include "simde/hedley.h"
@@ -14,22 +11,10 @@
 # ifdef OPENMP
 #  define SORT_PARALLEL ips4o::parallel::sort
 # else
-#   ifdef __APPLE__
-#    define SORT_PARALLEL ips4o::sort
-#   else
-#    define SORT_PARALLEL(first, last, ...) std::sort(std::execution::par, first, last, ##__VA_ARGS__)
-#   endif
+#  define SORT_PARALLEL ips4o::sort
 # endif
 # define SORT_SERIAL std::sort
 #else
-# ifdef __APPLE__
-#  define SORT_PARALLEL(first, last, ...) std::sort(first, last, ##__VA_ARGS__)
-# else
-#  define SORT_PARALLEL(first, last, ...) std::sort(std::execution::par, first, last, ##__VA_ARGS__)
-# endif
+# define SORT_PARALLEL std::sort
 # define SORT_SERIAL std::sort
 #endif
-
-
-
-