gcj: fix build with glibc 2.26

pkgs/development/compilers/gcc/6/default.nix

@@ -73,6 +73,7 @@ let version = "6.4.0";
       ++ optional langAda ../gnat-cflags.patch
       ++ optional langFortran ../gfortran-driving.patch
       ++ [ ../struct-ucontext.patch ../struct-sigaltstack.patch ] # glibc-2.26
+      ++ optional langJava [ ../struct-ucontext-libjava.patch ] # glibc-2.26
       ;
 
     javaEcj = fetchurl {

pkgs/development/compilers/gcc/struct-ucontext-libjava.patch

@@ -0,0 +1,33 @@
+--- a/libjava/include/x86_64-signal.h
++++ a/libjava/include/x86_64-signal.h
+@@ -28,7 +28,7 @@
+ #define HANDLE_DIVIDE_OVERFLOW						\
+ do									\
+ {									\
+-  struct ucontext *_uc = (struct ucontext *)_p;				\
++  ucontext_t *_uc = (ucontext_t *)_p;					\
+   gregset_t &_gregs = _uc->uc_mcontext.gregs;				\
+   unsigned char *_rip = (unsigned char *)_gregs[REG_RIP];		\
+ 									\
+--- a/libjava/include/i386-signal.h
++++ a/libjava/include/i386-signal.h
+@@ -29,7 +29,7 @@
+ #define HANDLE_DIVIDE_OVERFLOW						\
+ do									\
+ {									\
+-  struct ucontext *_uc = (struct ucontext *)_p;				\
++  ucontext_t *_uc = (ucontext_t *)_p;					\
+   gregset_t &_gregs = _uc->uc_mcontext.gregs;				\
+   unsigned char *_eip = (unsigned char *)_gregs[REG_EIP];		\
+ 									\
+--- a/libjava/include/s390-signal.h
++++ a/libjava/include/s390-signal.h
+@@ -51,7 +51,7 @@
+   struct                                                                \
+   {                                                                     \
+     unsigned long int uc_flags;                                         \
+-    struct ucontext *uc_link;                                           \
++    ucontext_t *uc_link;                                                \
+     stack_t uc_stack;                                                   \
+     mcontext_t uc_mcontext;                                             \
+     unsigned long sigmask[2];                                           \