Fix compiler error by renaming HAVE_UCONTEXT_H -> PHAVE_UCONTEXT_H

panda/src/pipeline/contextSwitch.c

@@ -19,7 +19,7 @@
 
 #ifdef THREAD_SIMPLE_IMPL
 
-#if defined(HAVE_UCONTEXT_H)
+#if defined(PHAVE_UCONTEXT_H)
 
 /* The getcontext() / setcontext() implementation.  Easy-peasy. */
 

panda/src/pipeline/contextSwitch.h

@@ -30,7 +30,7 @@
 
 #ifdef THREAD_SIMPLE_IMPL
 
-#if defined(HAVE_UCONTEXT_H)
+#if defined(PHAVE_UCONTEXT_H)
 /* We'd prefer to use getcontext() / setcontext() to portably change
    execution contexts within C code.  That's what these library
    functions are designed for. */