Fix CI hangs on win32

After much debugging, it turns out that OpenBlas is sometimes hanging
on exit due to bad assumptions in its thread management. The upstream
discussion is at OpenMathLib/OpenBLAS#2350, but this
should fix our frequent win32 CI failures in the meantime.

deps/blas.mk

@@ -99,7 +99,12 @@ $(BUILDDIR)/$(OPENBLAS_SRC_DIR)/openblas-skylakexdgemm.patch-applied: $(BUILDDIR
 		patch -p1 -f < $(SRCDIR)/patches/openblas-skylakexdgemm.patch
 	echo 1 > $@
 
-$(BUILDDIR)/$(OPENBLAS_SRC_DIR)/build-configured: $(BUILDDIR)/$(OPENBLAS_SRC_DIR)/openblas-skylakexdgemm.patch-applied
+$(BUILDDIR)/$(OPENBLAS_SRC_DIR)/openblas-winexit.patch-applied: $(BUILDDIR)/$(OPENBLAS_SRC_DIR)/source-extracted
+	cd $(BUILDDIR)/$(OPENBLAS_SRC_DIR) && \
+		patch -p1 -f < $(SRCDIR)/patches/openblas-winexit.patch
+	echo 1 > $@
+
+$(BUILDDIR)/$(OPENBLAS_SRC_DIR)/build-configured: $(BUILDDIR)/$(OPENBLAS_SRC_DIR)/openblas-skylakexdgemm.patch-applied $(BUILDDIR)/$(OPENBLAS_SRC_DIR)/openblas-winexit.patch-applied
 	echo 1 > $@
 
 $(BUILDDIR)/$(OPENBLAS_SRC_DIR)/build-compiled: $(BUILDDIR)/$(OPENBLAS_SRC_DIR)/build-configured

deps/patches/openblas-winexit.patch

@@ -0,0 +1,34 @@
+commit 67bdd1b07c8fe880b2813c96849444b3dea67860
+Author: Keno Fischer <[email protected]>
+Date:   Sun Dec 29 15:08:13 2019 -0500
+
+    win32: Don't run cleanup if we're about to exit anyway
+
+    If the process is about to exit, there's no point trying to do
+    a bunch of work to clean up resources. The kernel will release
+    them much more efficiently when the process exits at the end
+    of this function.
+
+diff --git a/exports/dllinit.c b/exports/dllinit.c
+index 02ff092e..b65fe0c6 100644
+--- a/exports/dllinit.c
++++ b/exports/dllinit.c
+@@ -42,13 +42,17 @@ void gotoblas_init(void);
+ void gotoblas_quit(void);
+
+ BOOL APIENTRY DllMain(HINSTANCE hInst, DWORD reason, LPVOID reserved) {
++<<<<<<< HEAD
+
+   if (reason == DLL_PROCESS_ATTACH) {
+     gotoblas_init();
+   }
+
+   if (reason == DLL_PROCESS_DETACH) {
+-    gotoblas_quit();
++    // If the process is about to exit, don't bother releasing any resources
++    // The kernel is much better at bulk releasing then.
++    if (!reserved)
++      gotoblas_quit();
+   }
+
+   return TRUE;