gcc 5-7: fix build error for x86 targets

building any of i?86, x86_64, and x32 targets on a *musl* host with a
recent gcc host version (in my testing gcc 11), fails due to attempt
to convert a pointer type (nullptr_t) implicitly to bool.

the issue affects the 3 supported gcc versions 5.3.0, 6.5.0 and 7.5.0.

patches/gcc-5.3.0/0022-i386-bool-null.diff

@@ -0,0 +1,11 @@
+--- gcc-6.5.0.orig/gcc/config/i386/i386.c
++++ gcc-6.5.0/gcc/config/i386/i386.c
+@@ -8747,7 +8747,7 @@
+ 			 HOST_WIDE_INT words)
+ {
+   int res = 0;
+-  bool error_p = NULL;
++  bool error_p = 0;
+ 
+   if (TARGET_IAMCU)
+     {

patches/gcc-6.5.0/0027-i386-bool-null.diff

@@ -0,0 +1,11 @@
+--- gcc-6.5.0.orig/gcc/config/i386/i386.c
++++ gcc-6.5.0/gcc/config/i386/i386.c
+@@ -8747,7 +8747,7 @@
+ 			 HOST_WIDE_INT words)
+ {
+   int res = 0;
+-  bool error_p = NULL;
++  bool error_p = 0;
+ 
+   if (TARGET_IAMCU)
+     {

patches/gcc-7.5.0/0024-i386-bool-null.diff

@@ -0,0 +1,11 @@
+--- gcc-6.5.0.orig/gcc/config/i386/i386.c
++++ gcc-6.5.0/gcc/config/i386/i386.c
+@@ -8747,7 +8747,7 @@
+ 			 HOST_WIDE_INT words)
+ {
+   int res = 0;
+-  bool error_p = NULL;
++  bool error_p = 0;
+ 
+   if (TARGET_IAMCU)
+     {