Adds back GCC 4.8 support

Author: grisumbras

Jamfile

@@ -11,15 +11,22 @@ import ../config/checks/config : requires ;
 
 # These make sure we only build on
 # compatible C++11 or later toolchains.
+obj check_basic_alignas : check/basic_alignas.cpp ;
+explicit check_basic_alignas ;
+
 constant c11-requires :
     [ requires
-    cxx11_alignas
     cxx11_constexpr
     cxx11_decltype
     cxx11_hdr_tuple
     cxx11_template_aliases
     cxx11_variadic_templates
     ]
+    # We only require limited alignas support,
+    # so we have to use a custom check
+    [ check-target-builds
+    ..//check_basic_alignas cxx11_basic_alignas : : <build>no
+    ]
     ;
 
 path-constant LIB_DIR : . ;

check/basic_alignas.cpp

@@ -0,0 +1,9 @@
+struct some_struct {
+    double d;
+    int n;
+    void* ptr;
+};
+
+alignas(16) char test1[10];
+alignas(double) char test2[10];
+alignas(some_struct) char test3[10];

fuzzing/Jamfile

@@ -22,6 +22,8 @@ else
     LIB = <library>/boost/json//boost_json ;
 }
 
+project : requirements $(c11-requires) ;
+
 # See the comments in CMakeLists.txt for why
 # these are libraries and not exe targets.
 lib fuzzerlib_basic_parser :