I use xmlsec1 in library configured with autotools but compilation fails with error message:

<command-line>:0:16: error: missing terminating " character

this usually is a warning but I have -Werror and it would fail anyway in different place as we can see for generic test

% cat test.c
#include <stdio.h>
int main()
{
	printf("%s\n",XMLSEC_CRYPTO);
}

% gcc `pkg-config --cflags xmlsec1-openssl` test.c
<command-line>:0:18: warning: missing terminating " character
test.c: In function ‘main’:
test.c:4:2: error: stray ‘\’ in program
test.c:4:2: error: stray ‘\’ in program
test.c:4:2: error: stray ‘\’ in program
test.c:4:2: error: missing terminating " character
test.c:4:29: error: expected expression before ‘)’ token

The cause is -DXMLSEC_CRYPTO=\\\"openssl\\\" in xmlsec1-openssl.pc.in (and other xmlsec1-*.pc.in files) which should be DXMLSEC_CRYPTO=\"openssl\".