check for and use C library provided strlcpy and strlcat

The musl-libc library provides implementations of strlcpy and strlcat,
so introduce a feature check for it and only use the kvmtool
implementation if there is no library support for it.
This avoids clashes with the public definition.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
diff --git a/Makefile b/Makefile
index 46e4a9d..285c482 100644
--- a/Makefile
+++ b/Makefile
@@ -199,6 +199,11 @@
 # On a given system, some libs may link statically, some may not; so, check
 # both and only build those that link!
 
+ifeq ($(call try-build,$(SOURCE_STRLCPY),$(CFLAGS),),y)
+	CFLAGS_DYNOPT	+= -DHAVE_STRLCPY
+	CFLAGS_STATOPT	+= -DHAVE_STRLCPY
+endif
+
 ifeq ($(call try-build,$(SOURCE_BFD),$(CFLAGS),-lbfd -static),y)
 	CFLAGS_STATOPT	+= -DCONFIG_HAS_BFD
 	OBJS_STATOPT	+= symbol.o
diff --git a/config/feature-tests.mak b/config/feature-tests.mak
index 6bee6c2..03cdb42 100644
--- a/config/feature-tests.mak
+++ b/config/feature-tests.mak
@@ -196,3 +196,13 @@
 	return 0;
 }
 endef
+
+define SOURCE_STRLCPY
+#include <string.h>
+
+int main(void)
+{
+	strlcpy(NULL, NULL, 0);
+	return 0;
+}
+endef
diff --git a/include/kvm/strbuf.h b/include/kvm/strbuf.h
index 2beefbc..7657339 100644
--- a/include/kvm/strbuf.h
+++ b/include/kvm/strbuf.h
@@ -6,8 +6,10 @@
 
 int prefixcmp(const char *str, const char *prefix);
 
+#ifndef HAVE_STRLCPY
 extern size_t strlcat(char *dest, const char *src, size_t count);
 extern size_t strlcpy(char *dest, const char *src, size_t size);
+#endif
 
 /* some inline functions */
 
diff --git a/util/strbuf.c b/util/strbuf.c
index 99d6b0c..2c6e8ad 100644
--- a/util/strbuf.c
+++ b/util/strbuf.c
@@ -13,6 +13,7 @@
 	}
 }
 
+#ifndef HAVE_STRLCPY
 /**
  * strlcat - Append a length-limited, %NUL-terminated string to another
  * @dest: The string to be appended to
@@ -60,3 +61,4 @@
 	}
 	return ret;
 }
+#endif