Use angle brackes for libc includes.

Cython/Includes/libc/errno.pxd

 # 7.5 Errors <errno.h>
 
-cdef extern from "errno.h" nogil:
+cdef extern from "<errno.h>" nogil:
     enum:
         EPERM
         ENOENT

Cython/Includes/libc/float.pxd

 # 5.2.4.2.2 Characteristics of floating types <float.h>
 
-cdef extern from "float.h":
+cdef extern from "<float.h>":
 
     const float FLT_RADIX
 

Cython/Includes/libc/limits.pxd

 # 5.2.4.2.1 Sizes of integer types <limits.h>
 
-cdef extern from "limits.h":
+cdef extern from "<limits.h>":
 
     enum: CHAR_BIT
     enum: MB_LEN_MAX

Cython/Includes/libc/locale.pxd

@@ -4,7 +4,7 @@
 from libc.string cimport const_char
 
 
-cdef extern from "locale.h" nogil:
+cdef extern from "<locale.h>" nogil:
 
     struct lconv:
         char *decimal_point

Cython/Includes/libc/math.pxd

-cdef extern from "math.h" nogil:
+cdef extern from "<math.h>" nogil:
     double M_E
     double e "M_E"  # as in Python's math module
     double M_LOG2E

Cython/Includes/libc/setjmp.pxd

-cdef extern from "setjmp.h" nogil:
+cdef extern from "<setjmp.h>" nogil:
     ctypedef struct jmp_buf:
         pass
     int setjmp(jmp_buf state)

Cython/Includes/libc/signal.pxd

@@ -2,7 +2,7 @@
 
 ctypedef void (*sighandler_t)(int SIGNUM) nogil
 
-cdef extern from "signal.h" nogil:
+cdef extern from "<signal.h>" nogil:
 
     ctypedef int sig_atomic_t
 
@@ -21,7 +21,7 @@ cdef extern from "signal.h" nogil:
     int          raise_"raise" (int signum)
 
 
-cdef extern from "signal.h" nogil:
+cdef extern from "<signal.h>" nogil:
 
     # Program Error
     enum: SIGFPE

Cython/Includes/libc/stddef.pxd

 # 7.17 Common definitions <stddef.h>
 
-cdef extern from "stddef.h":
+cdef extern from "<stddef.h>":
 
     ctypedef signed int ptrdiff_t
 

Cython/Includes/libc/stdint.pxd

@@ -2,7 +2,7 @@
 # Actual compile time size used for conversions.
 
 # 7.18 Integer types <stdint.h>
-cdef extern from "stdint.h" nogil:
+cdef extern from "<stdint.h>" nogil:
 
     # 7.18.1 Integer types
     # 7.18.1.1 Exact-width integer types

Cython/Includes/libc/stdio.pxd

@@ -5,7 +5,7 @@
 from libc.string cimport const_char, const_void
 
 
-cdef extern from "stdio.h" nogil:
+cdef extern from "<stdio.h>" nogil:
 
     ctypedef struct FILE
     cdef FILE *stdin

Cython/Includes/libc/stdlib.pxd

@@ -4,7 +4,7 @@
 from libc.string cimport const_char, const_void
 
 
-cdef extern from "stdlib.h" nogil:
+cdef extern from "<stdlib.h>" nogil:
 
     # 7.20.1 Numeric conversion functions
     int atoi (const char *string)

Cython/Includes/libc/string.pxd

@@ -7,7 +7,7 @@ cdef extern from *:
     ctypedef const unsigned char const_uchar "const unsigned char"
     ctypedef const void const_void "const void"
 
-cdef extern from "string.h" nogil:
+cdef extern from "<string.h>" nogil:
 
     void *memcpy  (void *pto, const void *pfrom, size_t size)
     void *memmove (void *pto, const void *pfrom, size_t size)

Cython/Includes/libc/time.pxd

@@ -2,7 +2,7 @@
 
 from libc.stddef cimport wchar_t
 
-cdef extern from "time.h" nogil:
+cdef extern from "<time.h>" nogil:
     ctypedef long clock_t
     ctypedef long time_t
 

Cython/Includes/libcpp/limits.pxd

-cdef extern from "limits" namespace "std" nogil:
+cdef extern from "<limits>" namespace "std" nogil:
    enum float_round_style:
         round_indeterminate       = -1
         round_toward_zero         = 0

Cython/Includes/openmp.pxd

-cdef extern from "omp.h":
+cdef extern from "<omp.h>":
     ctypedef struct omp_lock_t:
         pass
     ctypedef struct omp_nest_lock_t: