fix JuliaLang#42608, restore win32_ucontext.h in public headers list (JuliaLang#42612)

Author: JeffBezanson

src/Makefile

@@ -111,6 +111,9 @@ UV_HEADERS += uv.h
 UV_HEADERS += uv/*.h
 endif
 PUBLIC_HEADERS := $(BUILDDIR)/julia_version.h $(wildcard $(SRCDIR)/support/*.h) $(addprefix $(SRCDIR)/,julia.h julia_assert.h julia_threads.h julia_fasttls.h julia_locks.h julia_atomics.h jloptions.h)
+ifeq ($(OS),WINNT)
+PUBLIC_HEADERS += $(addprefix $(SRCDIR)/,win32_ucontext.h)
+endif
 HEADERS := $(PUBLIC_HEADERS) $(addprefix $(SRCDIR)/,julia_internal.h options.h timing.h) $(addprefix $(BUILDDIR)/,$(DTRACE_HEADERS) jl_internal_funcs.inc)
 PUBLIC_HEADERS += $(addprefix $(SRCDIR)/,julia_gcext.h)
 PUBLIC_HEADER_TARGETS := $(addprefix $(build_includedir)/julia/,$(notdir $(PUBLIC_HEADERS)) $(UV_HEADERS))