libvbisam: Fix bugs around `ecvt`

`ecvt` was used undeclared in `libvbisam/isdecimal.c`.

`__set_errno` was undefined.

packages/libvbisam/build.sh

@@ -3,6 +3,7 @@ TERMUX_PKG_DESCRIPTION="A replacement for IBM's C-ISAM"
 TERMUX_PKG_LICENSE="GPL-2.0, LGPL-2.1"
 TERMUX_PKG_MAINTAINER="@termux"
 TERMUX_PKG_VERSION=2.0
+TERMUX_PKG_REVISION=1
 TERMUX_PKG_SRCURL=https://downloads.sourceforge.net/project/vbisam/vbisam2/vbisam-${TERMUX_PKG_VERSION}.tar.gz
 TERMUX_PKG_SHA256=688b776e0030cce50fd7e44cbe40398ea93431f76510c7100433cc6313eabc4f
 

packages/libvbisam/efgcvt_r-template.c

@@ -30,6 +30,14 @@
 #define __FCVT_R fcvt
 #define __ECVT_R ecvt
 #define SNPRINTF snprintf
+#if __ANDROID_API__ >= 21
+static inline int
+__set_errno(int n)
+{
+  errno = n;
+  return -1;
+}
+#endif
 #endif
 
 #ifndef SNPRINTF
@@ -40,6 +48,8 @@
 #define APPEND(a, b) APPEND2 (a, b)
 #define APPEND2(a, b) a##b
 
+#pragma GCC visibility push(hidden)
+
 int
 __FCVT_R (FLOAT_TYPE value, int ndigit, int *decpt, int *sign,
 	  char *buf, size_t len)
@@ -203,3 +213,5 @@ __ECVT_R (FLOAT_TYPE value, int ndigit, int *decpt, int *sign,
   *decpt += exponent;
   return 0;
 }
+
+#pragma GCC visibility pop

packages/libvbisam/libvbisam-isdecimal.c.patch

@@ -0,0 +1,12 @@
+--- a/libvbisam/isdecimal.c
++++ b/libvbisam/isdecimal.c
+@@ -134,6 +134,9 @@
+ 	int		decpt;
+ 	int		sign;
+ 
++#ifdef __ANDROID__
++	char *ecvt(double, int, int *, int *);
++#endif
+ 	str = (unsigned char *)ecvt (dbl, ndigits, &decpt, &sign);
+ 
+ 	dp->dec_pos = sign ? 0 : 1;